#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
using namespace std;
long long int ncr[31][31];
int main() {
  long long int n, m, t, i, j, ans = 0;
  cin >> n >> m >> t;
  ncr[1][0] = ncr[1][1] = 1;
  for (i = 2; i <= 30; i++) {
    for (j = 0; j < i; j++) {
      ncr[i][j] = ncr[i - 1][j] + ncr[i - 1][j - 1];
    }
    ncr[i][i] = 1;
  }
  for (i = 4; i <= n; i++) {
    long long int temp = t - i;
    if (temp > m or temp < 1)
      continue;
    else
      ans = ans + ncr[n][i] * ncr[m][temp];
  }
  cout << ans;
}
