#include<stdio.h>
#define Nmax 5000010
int v[Nmax],deque[Nmax],N,K,st,dr;
long long S;                                                                        ;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&N,&K);

    for(int i=1;i<=N;++i)
        scanf("%d",&v[i]);

    st=1;
    dr=0;
    for(int i=1;i<=N;++i)
    {
        while(st<=dr && v[i]<=v[deque[dr]])
         --dr;
            deque[++dr]=i;

        if(deque[st]==i-K)
            ++st;

        if(i>=K)
        S=S+v[deque[st]];

    }
    printf("%lld",S);



    return 0;
}