#include <iostream>
#include <fstream>
using namespace std;
long N,K,i,st=0,dr=-1,suma=0,c[5000001];
int main(){
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>N>>K;
    long *v= new long[N];
    for (i=0;i<N;i++) f>>v[i];
    for (i=0;i<N;i++)
    {
        while (st<=dr && v[i]<=v[c[dr]])
            dr--;
        dr++;
        c[dr]=i;
        if (c[st]==i-K) st++;
        if (i+1>=K) suma=suma+v[c[st]];
    }
    g<<suma;
    delete []v;
    f.close();
    g.close();
    return 0;
}