#include <bits/stdc++.h>
using namespace std;
int conversion(string p) {
  int o;
  o = atoi(p.c_str());
  return o;
}
string toString(int h) {
  stringstream ss;
  ss << h;
  return ss.str();
}
long long gcd(long long a, long long b) { return (b == 0 ? a : gcd(b, a % b)); }
long long lcm(long long a, long long b) { return (a * (b / gcd(a, b))); }
int toi(string p) {
  int x;
  istringstream in(p);
  in >> x;
  return x;
}
int main() {
  long long a, b, c;
  cin >> a >> b >> c;
  cout << ((c + a - 1) * (b + a - 1) - (a * a - a)) << endl;
}
