#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

const int NMax = 5000000;

deque <int> dq;
int n, k;
long long ans;
int v[NMax + 5];

void Read(){
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
        fin >> v[i];
}

void Solve(){
    for (int i = 1; i <= n; i++){
        while (!dq.empty() && dq.front() < i - k + 1)
            dq.pop_front();
        while (!dq.empty() && v[dq.back()] > v[i])
            dq.pop_back();
        dq.push_back(i);
        if (i < k)
            continue;
        ans += v[dq.front()];
    }
}

void Print(){
    fout << ans << '\n';
}

int main(){
    Read();
    Solve();
    Print();
    return 0;
}