UVA10759_Dice Throwing

#include <iostream>
#include <cstdio>
#include <cstring>
typedef long long ll;
using namespace std;

ll f1[25][150],f2[25][150];
ll sum1[25][150],sum2[25][150];
int n,m;

ll gcd(ll A,ll B)
{
    return B==0?A:gcd(B,A%B);
}

ll lcm(ll A,ll B)
{
    return A/gcd(A,B)*B;
}

int main()
{
    f1[0][0]=f2[0][0]=sum1[0][0]=sum2[0][0]=1;
    for (int i=1; i<25; i++)
        for (int j=i; j<=i*6; j++)//i times score j
        {
            ll F1=0,F2=1,FF;
            for (int k=max(j-6,0); k<j; k++)
            {
                if (f1[i-1][k]==0) continue;
                FF=lcm(F2,f2[i-1][k]*6);
                F1=F1*(FF/F2)+f1[i-1][k]*(FF/(f2[i-1][k]*6));
                F2=FF;
                FF=gcd(F1,F2);
                F1/=FF,F2/=FF;
            }
            f1[i][j]=F1,f2[i][j]=F2;
            if (i==j)
            {
                sum1[i][j]=f1[i][j],sum2[i][j]=f2[i][j];
                continue;
            }
            FF=lcm(sum2[i][j-1],f2[i][j]);
            F1=sum1[i][j-1]*(FF/sum2[i][j-1])+f1[i][j]*(FF/f2[i][j]);
            sum1[i][j]=F1,sum2[i][j]=FF;
            FF=gcd(sum1[i][j],sum2[i][j]);
            sum1[i][j]/=FF,sum2[i][j]/=FF;
        }
    
    while (scanf("%d%d",&n,&m) && (n|m))
    {
        if (m<=n) puts("1");
        else if (m>6*n) puts("0");
        else printf("%lld/%lld\n",sum2[n][m-1]-sum1[n][m-1],sum2[n][m-1]);
    }  
    
    return 0;
}