#include <bits/stdc++.h>
int main() {
  int a, b, c;
  printf("please input integer:");
  scanf("%d", &a);
  scanf("%d", &b);
  if (a > 9 || b > 9)
    printf("c=-1\n");
  else {
    c = a * b;
    printf("%d\n", c);
  }
  return 0;
}
