decimal to binary

#include<bits/stdc++.h>
using namespace std;
int main()
{
    unsigned long y,z,i,a,b,j;
    cin>>y>>i>>j;
    string s;
   bitset<3999999>x(y);
  // cout<<x<<endl;
    i--;
   x[i] = j;
   unsigned long k = std::bitset<3999999>(x).to_ulong();
   cout<<k<<endl;

}