C++ :

#include<bits/stdc++.h>
using namespace std;
/*
	w(a,b,c)
	a<=0 || b<=0 || c<=0    w(a,b,c) = 1
	a>20 || b>20 || c>20    w(a,b,c)= w(20,20,20);
	w(a,b,c)=w(a-1,b,c)+w(a-1,b-1,c)+w(a-1,b,c-1)-w(a-1, b-1,c-l)
*/ 
int s[101][101][101];

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

int main(){
	int a,b,c;
	cin>>a>>b>>c;
	cout<<w(a,b,c);
	return 0;
}