N, K= map(int, input().split())
l = list(map(int, input().split()))
l.sort()
distance_l = []
for i in range(len(l) - 1):
    distance_l.append(l[i + 1] - l[i])
distance_l.sort()
ans = 0
for i in range(N - K):
    ans += distance_l[i]
print(ans)