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

        }
        while(st<=dr&&v[i]<=v[d[dr]])
        {
            dr--;
        }
        d[++dr]=i;
        if(i>=k-1)
        {
            s+=v[d[st]];
        }
    }
    o<<s;
}