UVa 10940 - Throwing Cards Away II

#include <bits/stdc++.h>
#define LL  long long
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(),(x).end()
#define REP(i,n) for(int i=0;i<n;i++)
#define FOR(i,a,b) for(int i=a;i<=b;i++)
#define pri(a) cout<<a<<endl
#define prii(a,b) cout<<a<<" "<<b<<endl
#define hi printf("Hello World\n")
#define pcs printf("CASE# %d:\n", ++cs);
#define WRITE(fn) freopen(fn, "w", stdout);
using namespace std;

int ar[5000009];

int main()
{
    int n, idx = 1;

    ar[idx++] = 1;

    int fl = 2, cnt = 2, go = 1;

    while(go < 5000005)
    {
        ar[idx++] = cnt;

        if(cnt==fl) fl*=2, cnt = 0;

        cnt+=2;

        go++;
    }
     while(cin>>n and n)
            printf("%d\n", ar[n]);

    return 0;
}