#include <stdio.h>
#include <stdlib.h>

long long v[5000010],deque[5000010];
long long i;
long long sum;
long long front,back,n,k;

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

    scanf("%lld %lld",&n,&k);


    for(i=1;i<=n;i++){
        scanf("%lld",&v[i]);
    }
    front=1;
    back=0;

    for(i=1;i<=n;i++){
        while(front<=back && v[i]<v[deque[back]]){
            back--;
        }
        back++;
        deque[back]=i;
        if(deque[front]==i-k){
            front++;
        }
        if(i>=k){
            sum+=v[deque[front]];
        }
    }
    printf("%lld",sum);
    return 0;
}