#include <cstdio>
#define MAXN 5000000
int sir[MAXN],dq[MAXN];
long long s;
int main()
{
    FILE *fin,*fout;
    fin=fopen("deque.in","r");
    fout=fopen("deque.out","w");
    int i,n,k,inc,sf;
    fscanf(fin,"%d%d",&n,&k);
    inc=sf=0;
    for(i=0;i<n;i++)
    {
        fscanf(fin,"%d",&sir[i]);
        while(inc<sf && sir[i]<sir[dq[sf-1]])
            sf--;
        dq[sf++]=i;
        if(dq[inc]==i-k)
            inc++;
        if(i>=k-1)
            s+=sir[dq[inc]];
    }
    fprintf(fout,"%lld",s);
    fclose(fin);
    fclose(fout);
    return 0;
}