#include <iostream>
#include <stdio.h>
using namespace std;
int v[5000001],d[5000001];
int main(){

    FILE *fin,*fout;
    fin=fopen("deque.in","r");
    fout=fopen("deque.out","w");

    int n,k,st,dr,s,i;

    fscanf(fin,"%d%d",&n,&k);

    st=1;
    dr=0;
    s=0;
    for(i=1;i<=n;i++){
        fscanf(fin,"%d",&v[i]);
        if(st<=dr&&d[st]==i-k)
            st++;
        while(st<=dr&&v[i]<=v[d[dr]])
            dr--;
        dr++;
        d[dr]=i;
        if(i>=k)
            s+=v[d[st]];
    }

    fprintf(fout,"%d",s);

    fclose(fin);
    fclose(fout);

    return 0;
}