diff --git a/du1/program.c b/du1/program.c
index e69de29..59af2fa 100644
--- a/du1/program.c
+++ b/du1/program.c
@@ -0,0 +1,29 @@
+#include <stdio.h>
+#include <ctype.h>
+
+int main() {
+    int c;
+    char output;
+    int count_line = 0;
+
+    while ((c = getchar()) != EOF) {
+        if (islower(c)) {
+            output = toupper(c);
+        }
+        else if (isupper(c)) {
+            output = tolower(c);
+        } 
+        else if (isgraph(c) || c == ' ') {
+            output = c;
+        }
+        else {
+            output = c; 
+        }
+        putchar(output);
+        if (c == '\n') { 
+            count_line++;
+        }
+    }
+   // printf("Number of lines: %d\n", count_line); 
+    return 0;
+}