#include <iostream>
#include <fstream>
#include <set>
#include <vector>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n, k;
long long sum;

set <int> subsec;
vector <int> copie;

void read(){
    fin>>n>>k;
    int nr=0;
    for(int i=1; i<=k; i++){
        int x;
        fin>>x;
        subsec.insert(x);
        copie.push_back(x);
    }
    sum+=*subsec.begin();
    for(int i=k+1; i<=n; i++){
        int x;
        fin>>x;
        subsec.erase(copie[i-k-1]);
        copie.push_back(x);
        subsec.insert(x);
        sum+=*subsec.begin();
    }
    fout<<sum;
}

int main()
{
    read();
    return 0;
}