#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, c;
  scanf("%d %d %d", &a, &b, &c);
  if (a > b) {
    swap(a, b);
  }
  if (a > c) {
    swap(a, c);
  }
  if (b > c) {
    swap(b, c);
  }
  printf("%d\n", b * (2 * a + b - 1) + (c - b - 1) * (a + b - 1));
  return 0;
}
