#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline const T MAX(T a, T b) {
  return ((a) > (b) ? (a) : (b));
}
template <typename T>
inline const T MIN(T a, T b) {
  return ((a) > (b) ? (b) : (a));
}
template <typename T>
inline const T ABS(T a) {
  return (((a) > 0) ? (a) : (-(a)));
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int a, b, c;
  cin >> a >> b >> c;
  cout << (a * b) + (b * c) + (c * a) - (a + b + c) + 1 << endl;
  return 0;
}
