#include <fstream>
#include <deque>

using namespace std;

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

deque <int> deq;

const int NMAX = 5e6 + 5;

int a[NMAX];

void solve(){
    long long sum = 0;
    int n, k;
    fin >> n >> k;
    for(int i = 1; i <= n; ++i){
        fin >> a[i];
    }
    for(int i = 1; i <= n; ++i){
        while(!deq.empty() && a[deq.back()] >= a[i]){
            deq.pop_back();
        }
        deq.push_back(i);
        if(!deq.empty() && deq.front() == i - k){
            deq.pop_front();
        }
        if(i >= k)
            sum += a[deq.front()];
    }
    fout << sum;
}

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