#include <bits/stdc++.h>
int main(void) {
  int A, B;
  scanf("%d%d", &A, &B);
  if (1 <= A <= 9 && 1 <= B <= 9) {
    printf("%d/n", A * B);
  } else if (10 <= A <= 20 || 10 <= B <= 20) {
    printf("-1/n");
  }
  return 0;
}
