code：

#include<iostream>
using namespace std;
long long flag[50][50][50];
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){
		if(flag[20][20][20] == -1){
			flag[20][20][20] = w(20,20,20);
		}
		return flag[20][20][20];
	}else if(a<b && b<c){
		if(flag[a][b][c] == -1){
			flag[a][b][c] = w(a,b,c-1)+w(a,b-1,c-1)-w(a,b-1,c);
		}
	}else{
		if(flag[a][b][c] == -1){
			flag[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-1);
		}
	}
	return flag[a][b][c];
}
int main(){
	long long a,b,c;
	for(int i = 0;i<=20;i++){
		for(int j = 0;j<=20;j++){
			for(int k = 0;k<=20;k++){
				flag[i][j][k] = -1;
			}
		}
	}
	scanf("%lld%lld%lld",&a,&b,&c);
	printf("w(%lld,%lld,%lld) = %lld\n",a,b,c,w(a,b,c));
	while(a!=-1&&b!=-1&&c!=-1){
		scanf("%lld%lld%lld",&a,&b,&c);
		if(a!=-1&&b!=-1&&c!=-1){
			printf("w(%lld,%lld,%lld) = %lld\n",a,b,c,w(a,b,c));
		}
	}
	return 0;
}