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