#include <bits/stdc++.h>
using namespace std;
long long fmin(long long a, long long b) { return a < b ? a : b; }
long long fmax(long long a, long long b) { return a > b ? a : b; }
int getBit(int n, int pos) { return (n >> pos) & 1; }
int main() {
  ios_base::sync_with_stdio(false);
  long long n, m, t;
  cin >> n >> m >> t;
  long long c[31][31];
  c[0][0] = 1;
  for (int i = 1; i <= 30; i++)
    for (int j = 0; j <= i; j++) {
      if (j == 0 || j == i)
        c[i][j] = 1;
      else
        c[i][j] = c[i - 1][j] + c[i - 1][j - 1];
    }
  long long sum = 0;
  for (int i = 4; i <= n; i++) {
    if (t - i <= m && t - i > 0) {
      long long z = c[n][i] * c[m][t - i];
      sum = sum + z;
    }
  }
  cout << sum;
}
