#include<stdio.h>
#include<vector>
#include<algorithm>
#include<iostream>
typedef long long ll;
int main()
{
	using namespace std;
	vector<ll> ar;
	using namespace std;
	ll t,i,k;
	ar.push_back(0);
	for(i=1;i<=500000;i++)
		{
			k=ar[i-1]-i;
			if((ar[i-1]-i)>0 && find(ar.begin(),ar.end(),k)==ar.end())
				ar.push_back(ar[i-1]-i);
				else
				ar.push_back(ar[i-1]+i);
		}
	while(scanf("%lld",&t)==1)
	{
		if(t==-1)
		break;
		printf("%lld\n",ar[t]);
	}
	return 0;
}

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

NwotMQ==

7
-1