#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  t = 1;
  while (t--) {
    long long n, i, j, w, h, count = 0, sum = 0, total, k, T, breaks = 0, a, b,
                             c;
    string s;
    cin >> a >> b >> c;
    cout << a * b + b * c + c * a - a - b - c + 1;
  }
}
