//zm.qz1z.com:2501
#include <bits/stdc++.h>
using namespace std;
int w(int a,int b,int c){
	if(a<=0||b<=0||c<=0) return 1;
	if(a>20||b>20||c>20) return w(20,20,20);
	if(a<=20&&a>0) return w(a-1,b,c)+w(a-1,b-1,c)+w(a-1,b,c-1)-w(a-1,b-1,c-1);
}
int main(){
	int n,m,k;
	cin>>n>>m>>k;
	cout<<w(n,m,k);
}
/**************************************************************
	Problem: 1690
	User: wangyiyang
	Language: C++
	Result: Time Limit Exceed
****************************************************************/