simple permutation

int permute(int n,int r)
{
    long long k=1,p=1;

    if(n-r<r)
    r=n-r;

     if(r)
     {
        while(r)
        {
            p*=n;
            k*=r;

            int m = __gcd(p,k);
            p/=m;
            k/=m;

            n--;
            r--;
        }
     }

    return p;


}