diff --git a/du1/program.c b/du1/program.c
new file mode 100644
index 0000000..a5b8e44
--- /dev/null
+++ b/du1/program.c
@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <ctype.h>
+#include <string.h>
+
+int main (){
+	char c[100];
+	char musor;
+	int counter = 0;
+	while(fgets(c, 100, stdin) != NULL){
+		if(strlen(c) == 1){
+			putchar (c[0]);
+			counter++;
+		}
+		else if(strlen(c) == 2){
+			if (c[0] >= 'a' && c[0] <= 'z'){
+				putchar (c[0] - 'a' + 'A');
+				printf ("\n");
+				counter++;
+			}
+			else if ( c[0] >= 'A' && c[0] <= 'Z'){
+				putchar (c[0] + 'a' - 'A');
+				printf ("\n");
+				counter++;
+			}
+			else if (!isalpha (c[0])) {
+				putchar (c[0]);
+				counter++;
+			}
+		}
+		else{
+			for(int i = 0; i < 100; i++){
+				if(c[i] == '\n' || c[i] == '\0') break;
+				if(isupper(c[i])) {
+                    printf("%c", tolower(c[i]));
+                }
+				else if(islower(c[i]))
+					printf("%c", toupper(c[i]));
+				else
+					printf("%c", c[i]);
+			}
+			if(strchr(c, '\n') != NULL){
+			    printf("\n");
+                counter++;
+			}
+		}
+		memset(c, '\0', 100);
+	}
+
+	printf("\nPočet riadkov: %d\n",counter);
+
+	return 0;
+}