The Recaman's sequence is defined by a₀ = 0 ; for m > 0, a_m = a_m−1 − m if the rsulting a_m is positive and not already in the sequence, otherwise a_m = a_m−1 + m.
The first few numbers in the Recaman's Sequence is 0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9 ...
Given k, your task is to calculate ak.

输入格式

The input consists of several test cases. Each line of the input contains an integer k where 0 <= k <= 500000.
The last line contains an integer −1, which should not be processed.

输出格式

For each k given in the input, print one line containing ak to the output.

样例输入

7
10000
-1

样例输出

20
18658

//C++98
#include <iostream>
#include <cstdio>
#include <map>
using namespace std;
long s[500005];
map<long ,bool>hash;
int main(){
    int p;
    long i,t;
    s[0] = 0;
    hash.clear();
    hash[0]=1;
    for(i=1; i<500003; i++){
        t = s[i-1]-i;
        if(t<=0 || hash[t])
            s[i] = s[i-1]+i;
        else
            s[i] = t;
        hash[s[i]] = true;
    }
    while(cin>>p && p!=-1)
        cout<<s[p]<<endl;
    return 0;
}