#include<iostream>
#include<fstream>
using namespace std;
#define nmax 5000001
int a[nmax],b[nmax],n,k,st,dr,i;
long s;

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    st=1;
    dr=0;
    for(i=1;i<=n;i++)
    {f>>a[i];
        while(st<=dr&&a[i]<=a[b[dr]]) dr--;
        dr++; b[dr]=i;
        if(b[st]==i-k) st++;
        if(i>=k) s+=a[b[st]];
    }
    g<<s;
    f.close();
    g.close();
    return 0;
}