C :

#include <stdio.h>
#include <string.h>
#include <math.h>
typedef long long LL;
LL x,y;
LL s;
int main(){
	while(~scanf("%lld",&x)){
		s=(LL)(log(x+1)/log(2.0));
		x=x-pow(2,s)+1;
		if(x==0)
			printf("%lld\n",(LL)(pow(2,s)-1));
		else
			printf("%lld\n",2*x-1);
	}
	return 0;
} 

C++ :

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    ll n;
    while(~scanf("%lld",&n)){
        ll len=0;
        ll ans=0;
        ll data=1;
        for (ll i=0;i<63;i++){
            if ((data<<i)>n){
                len=i-1;
                break;
            }
        }
        ans=(n-(data<<len));
        printf("%lld\n",(ans<<data)+data);
    }
    return 0;
}