#include<stdio.h>
int st=-1,dr,v[5000010],d[5000010],k,n,s;
void dreapta(int i)
{
    while(st<=dr&&v[i]<=v[d[dr]])
        dr--;
    d[++dr]=i;
}
inline void stanga(int i)
{
    if(d[st]==i-k)
        st++;
}
int main()
{
    FILE *in=fopen("deque.in","r"),*out=fopen("deque.out","w");
    int i;
    fscanf(in,"%d%d",&n,&k);
    for(i=1;i<=n;i++)
        fscanf(in,"%d",&v[i]);
    for(i=1;i<=n;i++)
    {
        if(i>k)
            stanga(i);
        dreapta(i);
        if(i>=k)
            s+=v[d[st]];
    }
    fprintf(out,"%d\n",s);
    return 0;
}