样例过了但是tle

#include <bits/stdc++.h> 
using namespace std;

long long w(long long a,long long b,long long c) 
{
    if (a <= 0||b <= 0||c <= 0)
    {
        return 1;
    }
    if (a > 20||b > 20||c > 20)
    {
        return w(20,20,20);
    }
    if (a < b&&b < c)
    {
        return (a,b,c-1) + w(a,b-1,c-1) - w(a,b-1,c);
    }
    else
    {
        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()
{
    long long a,b,c;
    while (1)
    {
        cin>>a>>b>>c;
        if(a == -1&&b == -1&&c == -1)
        {
            break;
        }
        cout<<"w("<<a<<","<<b<<","<<c<<") = "<<w(a,b,c)<<endl;
    }
    return 0;
}

搜索不太明白求指点？