#include <bits/stdc++.h>
int main() {
  int a, b, c;
  if (scanf("%d %d", &a, &b) == 2) {
    if (a < 1 || a > 10 || b < 1 || b > 10) {
      printf("-1\n");
    } else {
      c = a * b;
      printf("%d", c);
    }
  } else {
    printf("Failed to read integer.\n");
  }
  return 2;
}
