#include <bits/stdc++.h>
using namespace std;
int mod = 1e9 + 7;
bool isPrime(long long n) {
  for (long long i = 2; i <= sqrt(n); i++)
    if (n % i == 0) return false;
  return true;
}
int sod(long long x) {
  int res = 0;
  while (x) {
    int a = x % 10;
    res += a;
    x /= 10;
  }
  return res;
}
vector<long long> c[31];
void com() {
  c[1].push_back(1);
  c[1].push_back(1);
  for (int i = 2; i <= 30; i++) {
    c[i].push_back(1);
    for (int j = 1; j <= i - 1; j++)
      c[i].push_back(c[i - 1][j] + c[i - 1][j - 1]);
    c[i].push_back(1);
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  t = 1;
  while (t--) {
    long long n, m, t;
    cin >> n >> m >> t;
    long long res = 0;
    com();
    for (int i = n; i >= 4; i--)
      for (int j = m; j >= 1; j--)
        if (i + j == t) res += (c[n][i] * c[m][j]);
    cout << res << endl;
  }
}
