getting wrong in problem GUESS

Please,Can anybody tell what is going wrong in my code of problem GUESS?
My solution:www.codechef.com/viewsolution/7500878

`//probability
 
int main()
{
  ll t,m,n,num,den,i,a,num1,num2;
  sl(t);
  while(t--)
  {
    scanf("%lld %lld",&m,&n);
    num1=((m+1)/2)*(n/2);//used braces! though not needed here!
    num2=(m/2)*((n+1)/2);//used braces! ,else value needed may change (m/2)*(n+1)/2 not same as (m/2)*((n+1)/2)
    num=num1+num2;
    den=n*m;
    a=gcd(num,den);//can also use inbuild __gcd()
    num/=a;den/=a;
    printf("%lld/%lld\n",num,den);
 
  }
  return 0;
}
`
//