diff --git a/ones/Makefile b/ones/Makefile
new file mode 100755
index 0000000..cea1be0
--- /dev/null
+++ b/ones/Makefile
@@ -0,0 +1,15 @@
+EXE=a.out
+CC=gcc
+CFLAGS=-lm -lcrypt -O2 -Wall -Wextra -pipe -DONLINE_JUDGE
+OBJ=main.cpp
+
+.PHONY: clean test
+test: $(EXE)
+	./$(EXE) <d0 | diff --color=always a0 -
+
+
+$(EXE): $(OBJ)
+	$(CC) $(CFLAGS) -o $@ $(OBJ)
+
+clean:
+	rm -rf $(EXE)
diff --git a/ones/a0 b/ones/a0
new file mode 100644
index 0000000..fb29884
--- /dev/null
+++ b/ones/a0
@@ -0,0 +1,3 @@
+3
+6
+12
diff --git a/ones/d0 b/ones/d0
new file mode 100644
index 0000000..1c1ae31
--- /dev/null
+++ b/ones/d0
@@ -0,0 +1,3 @@
+3
+7
+9901
diff --git a/ones/main.cpp b/ones/main.cpp
new file mode 100644
index 0000000..3877e8f
--- /dev/null
+++ b/ones/main.cpp
@@ -0,0 +1,24 @@
+#include <cstdio>
+#include <cstdint>
+#include <cassert>
+
+int main()
+{
+    uint64_t N;
+    while (scanf("%lu\n", &N) != EOF)
+    {
+        uint64_t cmp = 1;
+        unsigned cmp_i = 1;
+        for (; cmp % N != 0 ;)
+        {
+            /*
+             *   11 = d+r
+             *  111 mod d === (d+r)*10 + 1 mod d === r10 + 1 mod d
+             */
+            cmp = (cmp % N) * 10 + 1;
+
+            ++cmp_i;
+        }
+        printf("%u\n", cmp_i);
+    }
+}