#include <bits/stdc++.h>
using namespace std;
long long fast_power(long long x, long long y) {
  if (y == 0) return 1;
  long long temp = fast_power(x, y / 2);
  temp = ((temp % 1000000007) * (temp % 1000000007)) % 1000000007;
  if (y % 2 != 0) temp = ((temp % 1000000007) * (x % 1000000007)) % 1000000007;
  return temp;
}
long long f[1000001];
long long inv[1000001];
long long ncr(long long n, long long r) {
  return ((((f[n] % 1000000007) * (inv[n - r] % 1000000007)) % 1000000007) *
          inv[r]) %
         1000000007;
}
long long nCr(long long n, long long r) {
  long long f = 1;
  long long x = 1;
  for (long long i = n; i > n - r; i--) {
    f *= i;
    f /= x++;
  }
  return f;
}
long long npr(long long n, long long r) {
  return (f[n] % 1000000007 * inv[n - r] % 1000000007) % 1000000007;
}
int main() {
  long long n, r, t;
  cin >> n >> r >> t;
  f[0] = 1;
  inv[0] = 1;
  for (long long i = 1; i <= n; i++) {
    f[i] = (f[i - 1] * i) % 1000000007;
    inv[i] = fast_power(f[i], 1000000007 - 2);
  }
  long long sum = 0;
  if (n >= 4)
    for (long long i = 4; i < t; i++) {
      if (t - i <= r) sum += nCr(n, i) * nCr(r, t - i);
    }
  cout << sum << "\n";
  return 0;
}
