diff --git a/2019/day04/INPUT.txt b/2019/day04/INPUT.txt
new file mode 100644
index 0000000..5891cc8
--- /dev/null
+++ b/2019/day04/INPUT.txt
@@ -0,0 +1 @@
+130254-678275
diff --git a/2019/day04/Makefile b/2019/day04/Makefile
new file mode 100644
index 0000000..30423a2
--- /dev/null
+++ b/2019/day04/Makefile
@@ -0,0 +1,92 @@
+# AOC daily Makefile - GNU make only.
+#
+# Copyright (C) 2021 Bruno Raoult ("br")
+# Licensed under the GNU General Public License v3.0 or later.
+# Some rights reserved. See COPYING.
+#
+# You should have received a copy of the GNU General Public License along with this
+# program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+#
+# SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+#
+
+INPUT   := INPUT.txt
+SHELL   := /bin/bash
+
+CC      := gcc
+
+LIB     := aoc_$(shell uname -m)
+INCDIR  := ../include
+LIBDIR  := ../lib
+LDFLAGS := -L$(LIBDIR)
+#LDLIB   := -l$(LIB) -lm
+LDLIB   := -l$(LIB)
+
+export LD_LIBRARY_PATH = $(LIBDIR)
+
+CFLAGS  += -std=gnu99
+CFLAGS  += -O2
+CFLAGS  += -g
+# for gprof
+#CFLAGS += -pg
+CFLAGS  += -Wall
+CFLAGS  += -Wextra
+CFLAGS  += -march=native
+# Next one may be useful for valgrind (some invalid instructions)
+# CFLAGS += -mno-tbm
+CFLAGS  += -Wmissing-declarations
+CFLAGS  += -Wno-unused-result
+
+CFLAGS  += -DDEBUG_DEBUG 	# activate general debug (debug.c)
+CFLAGS  += -DDEBUG_POOL		# memory pools management
+
+VALGRIND := valgrind
+VALGRINDFLAGS := -q -s --leak-check=full --show-leak-kinds=all --track-origins=yes
+
+
+TIME    := \time -f "\ttime: %E real, %U user, %S sys\n\tcontext-switch:\t%c+%w, page-faults: %F+%R\n"
+export PATH := .:$(PATH)
+
+.PHONY: clean all compile assembly memcheck memcheck1 memcheck2 ex1 ex2
+
+all: README.org ex1 ex2
+
+memcheck: memcheck1 memcheck2
+
+memcheck1: aoc-c
+	@$(VALGRIND) $(VALGRINDFLAGS) aoc-c -p 1 < $(INPUT)
+
+memcheck2: aoc-c
+	@$(VALGRIND) $(VALGRINDFLAGS) aoc-c -p 2 < $(INPUT)
+	@#@valgrind -s --track-origins=yes aoc-c -p 2 < $(INPUT)
+
+compile: aoc-c
+
+assembly: aoc-c.s
+
+ex1: aoc-c
+	@$(TIME) aoc-c -p 1 < $(INPUT)
+
+ex2: aoc-c
+	@$(TIME) aoc-c -p 2 < $(INPUT)
+
+clean:
+	@rm -f aoc-c core* vgcore* gmon.out aoc-c.s aoc-c.i README.html
+
+.c:
+	@echo compiling $<
+	@$(CC) $(CFLAGS) $(LDFLAGS) -I $(INCDIR) $< $(LDLIB) -o $@
+
+# generate pre-processed file (.i) and assembler (.s)
+%.i: %.c
+	@echo generating $@
+	@$(CC) -E $(CFLAGS) -I $(INCDIR) $< -o $@
+
+%.s: %.c
+	@echo generating $@
+	@$(CC) -S -fverbose-asm $(CFLAGS) -I $(INCDIR) $< -o $@
+
+# generate README.org from README.html (must cleanup !)
+%.org: %.html
+	@echo generating $@. Cleanup before commit !
+	@pandoc $< -o $@
diff --git a/2019/day04/README.org b/2019/day04/README.org
new file mode 100644
index 0000000..0d91e7a
--- /dev/null
+++ b/2019/day04/README.org
@@ -0,0 +1,24 @@
+** --- Day 4: Secure Container ---
+You arrive at the Venus fuel depot only to discover it's protected by a
+password. The Elves had written the password on a sticky note, but
+someone threw it out.
+
+However, they do remember a few key facts about the password:
+
+- It is a six-digit number.
+- The value is within the range given in your puzzle input.
+- Two adjacent digits are the same (like =22= in =122345=).
+- Going from left to right, the digits /never decrease/; they only ever
+  increase or stay the same (like =111123= or =135679=).
+
+Other than the range rule, the following are true:
+
+- =111111= meets these criteria (double =11=, never decreases).
+- =223450= does not meet these criteria (decreasing pair of digits
+  =50=).
+- =123789= does not meet these criteria (no double).
+
+/How many different passwords/ within the range given in your puzzle
+input meet these criteria?
+
+Your puzzle input is =130254-678275=.