Spoj solution to BALLSUM

BALLSUM.cpp

/* 
* @Author: Krishna
* @Date:   2015-12-20 04:38:55
* @Last Modified by:   Krishna
* @Last Modified time: 2015-12-20 06:44:20
*/

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <stack>
#include <queue>
#include <cmath>
#include <vector>
#include <set>
#include <omp.h>
#include <cstring>
#include <map>

#define ull unsigned long long
#define ll long long
#define sci(i) scanf("%d",&i)
#define scl(i) scanf("%ld",&i)
#define scll(i) scanf("%lld",&i)
#define rep(i,n) for(int i = 0; i < n; ++i)
#define loop(i,x,y) for(int i = x; i < y; ++i)

using namespace std;

typedef pair<int,int> pii;
typedef map<int,int> mii;
typedef map<int,int>::iterator miit;
int max (int a, int b) { return a > b ? a : b;}
int min (int a, int b) { return a < b ? a : b;}
ll gcd(ll a, ll b){ return (b==0)? a : gcd(b, a%b);}
int main() {
	ull n, k;
	while(true) {
		scll(n);
		scll(k);
		if(n == -1 && k == -1) break;
		else if(k <= 2) cout << 0 << endl;
		else {
			ll nn = (k-1)/2;
			ll p = nn*k - nn*(nn+1);
			//cout << p << endl;
			ll q;
			if(n & 1) 
				 q = ((n-1)/2) * n;
			else
				 q = (n/2) * (n-1); 
			//cout << p << " "  << q << endl;
			while(true) {
				ll g = gcd(p,q);
				if(g == 1) break;
				//cout <<"gcd:"<< g << endl;
				p /= g;
				q /= g;
				if(p == 1 || q == 1) break;
			}
			if(q == 1) printf("%lld\n", p);
			printf("%lld/%lld\n",p,q);
		}
	}
	//system("pause");
	return 0;
}