#include <bits/stdc++.h>
using namespace std;
int a[3], sum;
int main() {
  int i, j;
  scanf("%d%d%d", &a[0], &a[1], &a[2]);
  sort(a, a + 3);
  printf("%d\n", (a[1] + a[0] - 1) * (a[2] + a[0] - 1) - (a[0] - 1) * a[0]);
  return 0;
}
