#include <stdio.h>
int st,dr,k,n,v[5000001],d[5000001];
void stanga(int i){
    if(i-d[st]==k){
        st++;
    }
}
void dreapta(int i){
    while((st<=dr)&&(v[i]<=v[d[dr]])){
        dr--;
    }
}
int main(){
    int i;
    long long s=0;
    FILE *fin,*fout;
    fin=fopen("deque.in","r");
    fout=fopen("deque.out","w");
    fscanf(fin,"%d%d",&n,&k);
    for(i=1;i<=n;i++){
        fscanf(fin,"%d",&v[i]);
    }
    for(i=1;i<=n;i++){
        stanga(i);
        dreapta(i);
        dr++;
        d[dr]=i;
        if(i>=k){
            s+=v[d[st]];
        }
    }
    fprintf(fout,"%lld",s);
    return 0;
}