#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long a, b, c;
  cin >> a >> b >> c;
  cout << (a * b + b * c + c * a) - (a + b + c) + 1;
  return;
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  solve();
  return 0;
}
