import sys
input = lambda : sys.stdin.readline().rstrip()

sys.setrecursionlimit(2*10**5+10)
write = lambda x: sys.stdout.write(x+"\n")

n,k = list(map(int, input().split()))
a = list(map(int, input().split()))
ans = 0
x = a[0]
for i in range(n-k):
    ans += -1 * (a[n-1-i] - x)
for i in range(k):
    ans += (a[i] - x)
print(ans)