diff --git a/level05/source.c b/level05/source.c
new file mode 100644
index 0000000..2f66e5c
--- /dev/null
+++ b/level05/source.c
@@ -0,0 +1,15 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(void)
+{
+	char s[100];
+
+	fgets(s, 100, stdin);
+	for (size_t i = 0; i < strlen(s); ++i)
+		if (s[i] > 64 && s[i] <= 90)
+			s[i] ^= 32;
+	printf(s);
+	exit(0);
+}