#include<cstdio>
#include<set>
#include<string.h>
using namespace std;
const int MAX_K = 500005;
int number[MAX_K];
int k;

//使用set 2297ms
void init(){
     set<int> remember;
     number[0] = 0;
     remember.insert(0);
     int res = 0;
     for(int i = 1;i < MAX_K;++i){
          int now = number[i-1] - i;
          if(now < 0 || remember.count(now) == 1){
               now = number[i-1] + i;
               //printf("%lld\n",now);
          }
          number[i] = now;
          remember.insert(now);
          res = res > now ? res : now;
     }
     //printf("%d\n",res);//3012500
}
//知道最大值了，直接hash桶就完事了 16ms
bool use[3012505];
void init2(){
     number[0] = 0;
     memset(use,false,sizeof(use));
     use[0] = true;
     for(int i = 1;i < MAX_K;++i){
          int now = number[i-1] - i;
          if(now < 0 || use[now] == true){
               now = number[i-1] + i;
          }
          number[i] = now;
          use[now] = true;
     }
}
int main(){
     init2();
     while(~scanf("%d",&k) && k != -1){
          printf("%d\n",number[k]);
     }
     return 0;
}