#include<fstream.h>
#include<math.h>
ofstream f("sir.out");

float Ecuatie(int a, int b, int c)
{ int d;
  float x1,x2;
  d=b*b-4*a*c;
  if(d<0) return -32000;
  else if(d==0) { x1=-b/(2*a);
				  if(x1>0) return x1;
				  else return -32000;
				}
	   else { x1=(-b-sqrt(d))/(2*a);
			  x2=(-b+sqrt(d))/(2*a);
			  if(x1>x2) if(x1>0) return x1;
						else return -32000;
			  else if(x2>0) return x2;
				   else return -32000;
			}
}

void main()
{ int k,n;
  float x;
  cin>>k;
  x=Ecuatie(1,1,-2*k);
  n=floor(x);
  if(n==x) f<<n;
  else f<<k-n*(n+1)/2;
  f.close();
}