#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int INF=0x3f3f3f3f;
const ll LLINF=0x3f3f3f3f3f3f3f3fLL;
const int MAX=2e5+10;
const int mod=998244353;
int main()
{
	ll x,n,sq,cnt,i;
	scanf("%lld%lld",&x,&n);
	sq=sqrt(2*x);
	while((1+sq)*sq/2>=x) sq--;
	while((1+sq)*sq/2<=x) sq++;
	sq=min(sq-1,n);
	x-=(1+sq)*sq/2;
	x+=(n-sq)/2;
	for(i=sq+(n-sq)/2*2+1;i<=n;i++)
	{
		if(x<=0) x+=i;
		else x-=i;
	}
	printf("%lld\n",x);
	return 0;
}