#include<bits/stdc++.h>
using namespace std;
long long f[25][25][25];

long long w(long long a,long long b,long long c){
	if(a<=0||b<=0||c<=0) return 1;
    else if(a>20||b>20||c>20)return w(20,20,20);
	else if(f[a][b][c]!=0) return f[a][b][c];
	else if(a<b&&b<c)  f[a][b][c]=w(a,b,c-1)+w(a,b-1,c-1)-w(a,b-1,c);
	else f[a][b][c]=w(a-1,b,c)+w(a-1,b,c-1)-w(a-1,b-1,c-1);
	return f[a][b][c];
}

int main(){
long long d,f,g;
	while(cin>>d>>f>>g){
	memset(f,0,sizeof(f));
	 if(d == -1&&f == -1&&g == -1)break;
	 cout<<w(d,f,g);
    }
    return 0;
}