#include <bits/stdc++.h>
using namespace std;
void out() {
  cout << "Yes\n";
  exit(0);
}
const double eps = 1e-7;
const int N = 2e6 + 9;
int a, b, c;
int main() {
  ios::sync_with_stdio(false);
  cin >> a >> b >> c;
  cout << b * c + (b + c - 1) * (a - 1);
  return 0;
}
