#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    int x,n;
    cin>>x>>n;
    if(x >= 0){
    	if(n <= 2e9 && n*(n+1)/2 <= x){
    		cout<<x-n*(n+1)/2<<endl;
    		return 0;
    	}
    	int r = min((int)(2e9),n), l = 0;
    	while(r-l > 1){
    		int d = (l+r)/2;
    		if(d*(d+1)/2 > x) r = d;
    		else l = d;
    	}
    	int ans = x-(r*(r+1)/2);
    	ans -= (n-r)/2;
    	if((n-r)%2 == 1) ans += n;
    	cout<<ans<<endl;
    }
    else{
    	if(n <= 2e9 && n*(n+1)/2 <= -x){
    		cout<<x+n*(n+1)/2<<endl;
    		return 0;
    	}
    	int r = min((int)(2e9),n), l = 0;
    	while(r-l > 1){
    		int d = (l+r)/2;
    		if(d*(d+1)/2 > -x) r = d;
    		else l = d;
    	}
    	int ans = -x+(r*(r+1)/2);
    	ans += (n-r)/2;
    	if((n-r)%2 == 1) ans -= n;
    	cout<<ans<<endl;
    }
}