#include <bits/stdc++.h>
using namespace std;
const int Maxn = 33;
long long c[Maxn][Maxn];
void getC() {
  c[0][0] = 1;
  for (int i = 1; i < Maxn; ++i) {
    c[i][0] = 1;
    for (int j = 1; j < i; ++j) {
      c[i][j] = c[i - 1][j] + c[i - 1][j - 1];
    }
    c[i][i] = 1;
  }
}
int main() {
  getC();
  int n, m, t;
  scanf("%d%d%d", &n, &m, &t);
  long long ans = 0;
  for (int i = 4; i <= n; ++i) {
    if (i >= t) break;
    int j = t - i;
    if (j > m) continue;
    ans += c[n][i] * c[m][j];
  }
  cout << ans << endl;
  return 0;
}
