N, K = map(int, input().split())
A = list(map(int, input().split()))
A.sort()
diff = []
for i in range(N - 1):
    pos, nex = A[i], A[i + 1]
    diff.append(nex - pos)
# diff の中から大きいものK個取得する
diff.sort(reverse=True)
sumK = sum(diff[:(K - 1)])
ans = A[-1] - A[0] - sumK
print(ans)