#include <cstdio>
#include <deque>

using namespace std;

struct element{
    int val;
    int poz;
    element(int v, int p){
        val = v;
        poz = p;
    }
};

deque <element> deq;
int n;
int k;

void citire(){
    scanf("%d", &n);
    scanf("%d", &k);
    int s = 0;
    for(int i = 0; i < k; ++ i){
        int x;
        scanf("%d", &x);
        while(!deq.empty() && deq.back().val > x){
            deq.pop_back();
        }
        deq.push_back(element(x, i));
    }
    s += deq.front().val;
    for(int i = k; i < n; ++ i){
        int x;
        scanf("%d", &x);
        while(!deq.empty() && deq.back().val > x){
            deq.pop_back();
        }
        deq.push_back(element(x, i));
        if(deq.front().poz + k <= i){
            deq.pop_front();
        }
        s += deq.front().val;
    }
    printf("%d", s);

}

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

    citire();

    return 0;
}