#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[5000000],coada[5000000];
int main()
{
    int st=1,dr=0,n,i,x;
    long long s=0;
    in>>n>>x;
    for(i=1;i<=n;i++)
    {
        in>>v[i];
    }
    for(i=1;i<=n;i++)
    {
        while(st<=dr && v[i]<=v[coada[dr]])
            dr--;
        coada[++dr]=i;
        if(coada[st]==i-x)
            st++;
        if(i>=x)
            s=s+v[coada[st]];
    }
    out<<s;
    return 0;
}