diff --git a/du4/program.c b/du4/program.c
index 1c40cdc..cd09970 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -10,7 +10,7 @@ int main(){
     float z;
     char znamienko;
 
-    while(fgets(vstup, 100, stdin)!=NULL || *vstup!='\n'){
+    while(fgets(vstup, 100, stdin)!=NULL && *vstup!='\n'){
         if(sscanf(vstup, "%f %c %f = %f", &x, znamienko ,&y ,&z)!=4){
             printf("CHYBA\n");
             continue;