diff --git a/2020/RESULTS.txt b/2020/RESULTS.txt
index 18ac875..7783ef8 100644
--- a/2020/RESULTS.txt
+++ b/2020/RESULTS.txt
@@ -495,11 +495,19 @@ ex1.bash: res=75893264
 	time: 0:00.01 real, 0.01 user, 0.00 sys
 	context-switch:	0+1, page-faults: 0+166
 
+aoc-c : res=75893264
+	time: 0:00.00 real, 0.00 user, 0.00 sys
+	context-switch:	0+1, page-faults: 0+83
+
 +++++++++++++++++ ex2
 ex2.bash: res=38162588308
 	time: 6:52.50 real, 412.30 user, 0.14 sys
 	context-switch:	2219+1, page-faults: 0+30233
 
+aoc-c : res=38162588308
+	time: 0:01.33 real, 1.32 user, 0.01 sys
+	context-switch:	3+1, page-faults: 0+3992
+
 =========================================
 ================= day24 =================
 =========================================
diff --git a/2020/day23/aoc-c.c b/2020/day23/aoc-c.c
new file mode 100644
index 0000000..42b141e
--- /dev/null
+++ b/2020/day23/aoc-c.c
@@ -0,0 +1,116 @@
+/* aoc-c.c: Advent2020, day 23, part 1
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <ctype.h>
+
+#include "list.h"
+#include "debug.h"
+
+/* Here we will simply use an array for the numbers (as key is the number
+ * itself). All elements make a next/prev ring.
+ * Note: we will ignore array[0] to avoid millions of useless "position -1"
+ * calculations
+ */
+
+struct list_head *curcup;                         /* curcup cup */
+struct list_head *cups;                           /* the cups cups */
+int lastnum;                                      /* last cup number */
+
+#define CUR_CUP (&*curcup)
+#define NUM(pcup)  ((pcup) - cups)
+
+static __always_inline void step()
+{
+    struct list_head *first, *last, *dest = CUR_CUP;
+    int num[3] = { 0 };
+
+    first = CUR_CUP->next;
+    last  = first->next->next;
+    num[0] = NUM(first);
+    num[1] = NUM(first->next);
+    num[2] = NUM(last);
+
+    do {
+        if (NUM(--dest) <= 0)
+            dest = &cups[lastnum];
+    } while (NUM(dest) == num[0] || NUM(dest) == num[1] || NUM(dest) == num[2]);
+
+    //list_bulk_move_tail(dest->next, first, last);
+    list_bulk_move(dest, first, last);
+    curcup = CUR_CUP->next;
+}
+
+/**
+ * parse - initialize cups list.
+ */
+static void parse(int last)
+{
+    int count = 0, c;
+    cups = malloc(sizeof(struct list_head) * (last + 1));
+
+    if (cups) {
+        for (c = getchar();  isdigit(c); c = getchar(), ++count) {
+            struct list_head *next = &cups[c - '0'];
+            if (!count)                           /* first cup */
+                INIT_LIST_HEAD(curcup = next);
+            else
+                list_add_tail(&cups[c - '0'], CUR_CUP);
+        }
+        for (++count; count <= last; ++count)     /* add remaining cups */
+            list_add_tail(&cups[count], CUR_CUP);
+    }
+}
+
+static long part1()
+{
+    struct list_head *cur;
+    int res = 0;
+    list_for_each(cur, &cups[1]) {
+        res = res * 10 + NUM(cur);
+    }
+    return res;
+}
+
+static long part2()
+{
+    return NUM((&cups[1])->next) * NUM((&cups[1])->next->next);
+}
+
+static int usage(char *prg)
+{
+    fprintf(stderr, "Usage: %s [-d debug_level] [-p part]\n", prg);
+    return 1;
+}
+
+int main(ac, av)
+    int ac;
+    char **av;
+{
+    int opt, part = 1;
+
+    while ((opt = getopt(ac, av, "d:p:")) != -1) {
+        switch (opt) {
+            case 'd':
+                debug_level_set(atoi(optarg));
+                break;
+            case 'p':                             /* 1 or 2 */
+                part = atoi(optarg);
+                if (part < 1 || part > 2)
+            default:
+                    return usage(*av);
+        }
+    }
+
+    lastnum = part == 1? 9: 1000000;
+    int loops = part == 1? 100: 10000000;
+    parse(lastnum);
+    for (int i = 0; i < loops; ++i)
+        step();
+    printf("%s : res=%ld\n", *av, part == 1? part1(): part2());
+    free(cups);
+    exit (0);
+}