#include <bits/stdc++.h>
using namespace std;
using INT = long long;
using VI = vector<int>;
using pii = pair<int, int>;
template <typename A, typename B>
void smin(A &a, const B &b) {
  if (a > b) a = b;
}
template <typename A, typename B>
void smax(A &a, const B &b) {
  if (a < b) a = b;
}
int main() {
  int a, b, c;
  scanf("%d %d %d", &a, &b, &c);
  printf("%d\n", (b + c - 1) * (a - 1) + b * c);
}
