#include <cstdio>
#include <iostream>

int q[500010][2],pq=0,uq=-1;

int main()
{
    int n,k,i,x;
    long long s;
    FILE *f=fopen("deque.in","r");
    fscanf(f,"%d%d",&n,&k);
    for(i=1;i<=k;i++)
    {
        fscanf(f,"%d",&x);
        while(pq<=uq && x<=q[uq][0])uq--;
        q[++uq][0]=x;
          q[uq][1]=i;
    }
    s=q[pq][0];
    for(i=k+1;i<=n;i++)
    {
        if(q[pq][1]<=i-k)pq++;
        fscanf(f,"%d",&x);
        while(pq<=uq && x<=q[uq][0])uq--;
        q[++uq][0]=x;
          q[uq][1]=i;
        s+=q[pq][0];
    }
    fclose(f);
    f=fopen("deque.out","w");
    fprintf(f,"%lld",s);
    return 0;
}