diff --git a/du3/program.c b/du3/program.c
index 28d8cee..b4c380c 100644
--- a/du3/program.c
+++ b/du3/program.c
@@ -89,6 +89,11 @@ int main()
         while (fgets(input,sizeof(input),stdin)!=NULL)
         {	
             int flag=switch_operators(input);
+	    if((input[0]>=0 && input[0]<=47 && input[0]!=43 && input[0]!=45 && input[0]!=42 && input[0]!=47 && (input[0]<48 || input[0]>57)) || (input[0]>=58 && input[0]<=127))
+{
+    printf("bad input\n");
+    return 0;
+}
             input[strcspn(input,"\n")]=0;
             if (flag==0 || flag==-1)
             {