#include <bits/stdc++.h>
using namespace std;
int a, b, c;
int main() {
  cin >> a >> b >> c;
  cout << (a - 1) * (b - 1) + (a - 1) * (c - 1) + (b - 1) * (c - 1) + (a - 1) +
              (b - 1) + (c - 1) + 1;
  return 0;
}
