combinatorics.

//Author: Fuadul Hasan(fuadul202@gmail.com)
//BSMRSTU,Gopalganj
#include<bits/stdc++.h>
using namespace std;int tc = 1;
#define happy ios::sync_with_stdio(false);
#define coding  cin.tie(0);
#define pb  push_back
#define mp make_pair
#define ll long long
#define pr pair<int, int> 
#define vpr vector<pr> 
#define vi std::vector<int>
#define vll std::vector<ll>
#define all(n) n.begin(),n.end()
#define Test printf("Case %d: ",tc++);
#define YES printf("YES\n");
#define NO printf("NO\n");
#define Yes printf("Yes\n");
#define No printf("No\n");
const int mod = 1e9 + 7;
const ll  Inf = (ll)2e18 + 5;
const int N   = 2e5 + 5;

ll comb[31][31];

ll nCr(ll n,ll r){
	if(r>n) return 0LL;
	if(r==0||n==r) return 1LL;
	if(comb[n][r]) return comb[n][r];
	return comb[n][r] = nCr(n-1,r)+nCr(n-1,r-1);
}

/*ll nCr(ll n,ll r){
	ll ans  =1, t = 1;
	if(n<r) return 0;
	for(ll i = n;i>r;i--){
		ans*=i;
		ans/=t++;
	}
	return ans;
}*/

int solve() 
{
	//happy coding
	ll a,b,c;
	cin>>a>>b>>c;

	//combination..
	ll cele = 4;
	ll sum = 0;
	while(c-cele>=1){
		if(cele<=a&&c-cele<=b)
			sum += nCr(a,cele)*nCr(b,c-cele);
		//cout<<sum<<endl;
		cele++;
	}
	//ll sum = combination(30,4,30,26);

	cout<<sum<<endl;

	return 0;
}
int main(){
	int test = 1;
	//scanf("%d", &test);
	while (test--)solve();return 0;
}