#include <stdio.h>
int v[5000000],coada[5000000];
int main()
{
    FILE *fin,*fout;
    fin=fopen("deque.in","r");
    fout=fopen("deque.out","w");
    int n,k,i;
    fscanf(fin,"%d%d",&n,&k);
    for(i=0; i<n; i++)
        fscanf(fin,"%d",&v[i]);
    int st=1,dr=0;
    long long s=0;
    for(i=0; i<n; i++)
    {
        while(st<=dr&&v[i]<=v[coada[dr]])
            dr--;
        dr++;
        coada[dr] = i;
        if (coada[st] == i-k)
            st++;
        if (i+1>=k)
            s+=v[coada[st]];
    }
    fprintf(fout,"%lld\n",s);
    return 0;
}