from sys import stdin
##  input functions for me
def ria(sep = ''):
    if sep == '' :
        return list(map(int, input().split())) 
    else: return list(map(int, input().split(sep)))
def rsa(sep = ''):
    if sep == '' :
        return input().split() 
    else: return input().split(sep)
def ri(): return int(input())
def rd(): return float(input())
def rs(): return input()
##

## main ##
N, K = map(int, input().split())
F = N * (N + 1) // 2
M = F - 2 * (K * (N + N - 1 * (K - 1)) // 2)
print ((F - M) // 2 + 1)