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