#include <stdio.h>
#include <stdlib.h>
#define MAXN 1000000

#define BUF_SIZE 16384
char buf[BUF_SIZE];
int pbuf=BUF_SIZE;
FILE*fi,*fo;
inline char nextch(){
    if(pbuf==BUF_SIZE){
        fread(buf, BUF_SIZE, 1, fi);
        pbuf=0;
    }
    return buf[pbuf++];
}
inline long long nextnum(){
    long long a=0;
    char c=nextch();
    while((c<'0' || c>'9') && c!='-')
        c=nextch();
    int semn=1;
    if(c=='-'){
        semn=-1;
        c=nextch();
    }
    while('0'<=c && c<='9'){
        a=a*10+c-'0';
        c=nextch();
    }
    return a*semn;
}

struct element{
    int poz;
    int val;
} deque[5000000];
int main(){
    fi=fopen("deque.in","r");
    fo=fopen("deque.out","w");
    int n=nextnum(), k=nextnum();
    int p, u;
    p=u=0;
    long long s=0;
    int i;
    for(i=1;i<=k;i++){
        deque[u].val=nextnum();
        deque[u++].poz=i;
        while(u>p+1 && deque[u-1].val<deque[u-2].val){
            deque[u-2]=deque[u-1];
            u--;
        }
        if(i-deque[p].poz>=k)
            p++;
    }
    s=deque[p].val;
    while(i<=n){
        deque[u].val=nextnum();
        deque[u++].poz=i;
        while(u>p+1 && deque[u-1].val<deque[u-2].val){
            deque[u-2]=deque[u-1];
            u--;
        }
        if(i-deque[p].poz>=k)
            p++;
        //for(int j=p;j<u;j++)
        //    printf("%d ", deque[j].val);
        //printf("\n");
        s+=deque[p].val;
        i++;
    }
    fprintf(fo,"%lld", s);
    fclose(fi);
    fclose(fo);
    return 0;
}