#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, c;
  cin >> a >> b >> c;
  vector<int> ivec;
  ivec.push_back(a);
  ivec.push_back(b);
  ivec.push_back(c);
  sort(ivec.begin(), ivec.end());
  a = ivec[0];
  b = ivec[1];
  c = ivec[2];
  cout << (2 * a + b - 1) * b + (a + b - 1) * (c - 1 - b) << endl;
  return 0;
}
