#include<fstream>
#include<iostream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int v[50001],d[50001],n,k,st,dr;
long long suma;

int main () {


    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>v[i];
   st=1;
   dr=0;
    for(int i = 1; i <=n; i++)
        {
        while(dr >= st && v[i] <= v[d[dr]]) dr--;
        dr++;
        d[dr] = i;
        if(i >= k)
            {
            suma+= v[d[st]];
            if(d[st] == i - k + 1) {
                st++;
            }
        }
    }

    g<<suma;

    return 0;
}