#include <bits/stdc++.h>
using namespace std;
bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
long long int modulo(long long int x) {
  return ((x % +1000000007) % 1000000007);
}
long long int add_mod(long long int a, long long int b) {
  return modulo(modulo(a) + modulo(b));
}
long long int mul_mod(long long int a, long long int b) {
  return modulo(modulo(a) * modulo(b));
}
void _print(long long int t) { cout << t; }
void _print(int t) { cout << t; }
void _print(string t) { cout << t; }
void _print(char t) { cout << t; }
void _print(long double t) { cout << t; }
void _print(double t) { cout << t; }
void _print(unsigned long long t) { cout << t; }
template <class T, class V>
void _print(pair<T, V> p);
template <class T>
void _print(vector<T> v);
template <class T>
void _print(set<T> v);
template <class T, class V>
void _print(map<T, V> v);
template <class T>
void _print(multiset<T> v);
template <class T, class V>
void _print(pair<T, V> p) {
  cout << "{", _print(p.first), cout << ",", _print(p.second), cout << "}";
}
template <class T>
void _print(vector<T> v) {
  cout << "[ ";
  for (T i : v) _print(i), cout << " ";
  cout << "]";
}
template <class T>
void _print(set<T> v) {
  cout << "[ ";
  for (T i : v) _print(i), cout << " ";
  cout << "]";
}
template <class T>
void _print(multiset<T> v) {
  cout << "[ ";
  for (T i : v) _print(i), cout << " ";
  cout << "]";
}
template <class T, class V>
void _print(map<T, V> v) {
  cout << "[ ";
  for (auto i : v) _print(i), cout << " ";
  cout << "]";
}
void solve() {
  int a, b, c;
  cin >> a >> b >> c;
  cout << a * b + b * c + a * c - a - b - c + 1;
}
signed main() {
  ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
  long long int t = 1;
  for (long long int i = 1; i <= t; i++) {
    solve();
  }
  return 0;
}
