class SegTree(object):
    def __init__(self, N, op_data, u_data):
        self._n = N
        self.log = (N-1).bit_length()
        self.size = 1 << self.log

        self.op = op_data
        self.e = u_data

        self.data = [u_data] * (2 * self.size)
        # self.len = [1] * (2 * self.size)

    def __repr__(self):
        res = [self.get(i) for i in range(self._n)]
        return " ".join(map(str, res))

    def _update(self, i):
        self.data[i] = self.op(self.data[i << 1], self.data[i << 1 | 1])

    def initialize(self, arr=None):
        """ segtreeをarrで初期化する。len(arr) == Nにすること """
        if arr:
            for i, a in enumerate(arr, self.size):
                self.data[i] = a
        for i in reversed(range(1, self.size)):
            self._update(i)
            # self.len[i] = self.len[i << 1] + self.len[i << 1 | 1]

    def update(self, p, x):
        """ data[p] = x とする (0-indexed)"""
        p += self.size
        self.data[p] = max(x, self.data[p])
        for i in range(1, self.log + 1):
            self._update(p >> i)

    def get(self, p):
        """ data[p]を返す """
        return self.data[p + self.size]

    def prod(self, l, r):
        """
        op_data(data[l], data[l+1], ..., data[r-1])を返す (0-indexed)
        """
        sml = self.e
        smr = self.e
        l += self.size
        r += self.size

        while l < r:
            if l & 1:
                sml = self.op(sml, self.data[l])
                l += 1
            if r & 1:
                r -= 1
                smr = self.op(self.data[r], smr)
            l >>= 1
            r >>= 1
        return self.op(sml, smr)

    def all_prod(self):
        """ op(data[0], data[1], ... data[N-1])を返す """
        return self.data[1]


def main():
    N, K = map(int, input().split())
    A = list(map(int, input().split()))
    S = [0] * (N + 3)
    for i, a in enumerate(A, 1):
        S[i] = S[i-1] + a

    seg = SegTree(N + 3, max, -10**18)
    seg.update(0, 0)
    ans = 0
    for i in range(1, N + 1):
        L = max(0, i-K+1)
        dp = seg.prod(L, i) + S[i]
        ans = max(ans, dp)
        if i + 1 <= N:
            seg.update(i+1, dp - S[i+1])
        if i+2 <= N:
            seg.update(i+2, dp - S[i+2])

    print(ans)


main()