Codeforces Round #384 (Div. 2)/B. Chloe and the sequence

Problem:http://codeforces.com/contest/743/problem/B
Code:

#include<bits/stdc++.h>
using namespace std;

int main(){
 long long n,k;
 cin>>n>>k;
 cout<<__builtin_ffsll(k);
}