#include <stdio.h>
#define NMAX 5000001

int n, k, numbers[NMAX];
int dq[NMAX], head = 0, tail = -1;
long long ans;

void dqPushBack(int x) {
    while(tail >= head && numbers[dq[tail]] >= numbers[x])
        --tail;
    dq[++tail] = x;
}

int dqFront() {
    return dq[head];
}

void dqPop() {
    ++head;
}

int main() {
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    scanf("%d%d", &n, &k);
    for(int i = 0; i < n; ++i)
        scanf("%d", &numbers[i]);

    for(int i = 0; i < n; ++i) {
        dqPushBack(i);
        while(dqFront() == i - k) dqPop();
        if(i >= k - 1) ans += numbers[dqFront()];
    }

    printf("%lld", ans);

    return 0;
}