diff --git a/du3/program.c b/du3/program.c
index 11720c4..e931095 100644
--- a/du3/program.c
+++ b/du3/program.c
@@ -89,6 +89,11 @@ int main()
         char input[1000];
         while (fgets(input,sizeof(input),stdin)!=NULL)
         {
+		if((input[0]>'A' && input[0]<'Z') || (input[0]>'a' && input[0]<'z'))
+		{
+			printf("bad input\n");
+			return 0;
+		}	
             int flag=switch_operators(input);
             input[strcspn(input,"\n")]=0;
             if (strlen(input)==0 || input[0]==' ')