#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int coada[5000001],v[5000001];
int main(){
    int n,k,inc=0,sf=0,i;
    long long s=0;
    fin>>n>>k;
    v[0]=-10000001;
    for (i=1;i<=n;i++){
        fin>>v[i];
        if (i<k){
            while (v[i]<v[coada[sf]]&&inc<=sf)
                sf--;
            coada[++sf]=i;
        }
        else {
            if (i-k>=coada[inc])
                inc++;
            while (v[i]<v[coada[sf]]&&inc<=sf)
                sf--;
            coada[++sf]=i;
            s+=v[coada[inc]];
        }
    }
    fout<<s;
    return 0;
}