#include <bits/stdc++.h>
using namespace std;

int main() {
    long long x, n;
    scanf("%lld %lld", &x, &n);
    long long s;
    if(x == 0) { s = 0; }
    else if(x <= 0) {
        long long ng(0LL), ok(2000000000LL);
        while(1 < ok-ng) {
            long long mid((ok+ng)/2);
            if(mid & 1) {
                if(-x < (mid+1) / 2 * mid) {
                    ok = mid;
                }else {
                    ng = mid;
                }
            }else {
                if(-x < mid / 2 * (mid+1)) {
                    ok = mid;
                }else {
                    ng = mid;
                }
            }
        }
        s = ng;
    }else {
        long long ng(0LL), ok(2000000000LL);
        while(1 < ok-ng) {
            long long mid((ok+ng)/2);
            if(mid & 1) {
                if(x <= (mid+1) / 2 * mid) {
                    ok = mid;
                }else {
                    ng = mid;
                }
            }else {
                if(x <= mid / 2 * (mid+1)) {
                    ok = mid;
                }else {
                    ng = mid;
                }
            }
        }
        s = ok;
    }
    long long ans;
    if(n <= s) {
        if(n & 1) {
            if(0 < x) {
                ans = x - (n+1) / 2 * n;
            }else {
                ans = x + (n+1) / 2 * n;
            }
        }else {
            if(0 < x) {
                ans = x - n / 2 * (n+1);
            }else {
                ans = x - n / 2 * (n+1);
            }
        }
    }else {
        if(0 < x) {
            if(s & 1) {
                x = x - (s+1) / 2 * s;
            }else {
                x = x - s / 2 * (s+1);
            }
        }else {
            if(s & 1) {
                x = x + (s+1) / 2 * s;
            }else {
                x = x + s / 2 * (s+1);
            }
        }
        if((n-s) & 1) {
            ans = -x + (n-s) / 2 + 1;
        }else {
            ans = x - (n-s) / 2;
        }
    }
    printf("%lld\n", ans);
    return 0;
}