UVA 11971 - Polygon

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <string>
#include <map>
#include <vector>
#include <set>
#include <queue>
#include <stack>
#include <cctype>
using namespace std;
#define ll long long
typedef unsigned long long ull;
#define maxn 100000+100
#define INF 1<<30
ll gcd(ll a, ll b){
    return b ? gcd(b,a%b) : a;
}
ll pow_(ll a, ll b){
    if(b == 0)
        return 1;
    ll x = pow_(a, b/2);
    ll ans = x*x;
    if(b % 2 == 1)
        ans = ans * a;
    return ans;
}
int main (){
    ll up[60];
    ll down[60];
    for(ll i = 1; i <= 50; i++){
        ll z = pow_(2,i);
        ll a = z - (i+1);
        ll b = z;
        if(a != 0){
            ll x = gcd(a,b);
            a /= x;
            b /= x;
        }
        if(a == 0)
            b = 1;
        up[i] = a;
        down[i] = b;
    }
    ll num;
    ll counts = 0;
    scanf("%lld",&num);
    while(num--){
        ll n,k;
        scanf("%lld%lld",&n,&k);
        printf("Case #%lld: %lld/%lld\n",++counts,up[k],down[k]);
    }
    return 0;
}