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

using namespace std;

const int maxn = 5000005;

int n, k, a[maxn];
deque <int> d;

int main() {
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> n >> k;
    long long sum = 0;
    for(int i = 1 ; i <= n ; ++ i) {
        fin >> a[i];
        while(!d.empty() && a[d.back()] >= a[i])
            d.pop_back();
        d.push_back(i);
        if(i - d.front() >= k)
            d.pop_front();
        //cerr << a[d.front()] << ' ';
        if(i >= k)
            sum +=a[d.front()];
    }
    fout << sum << '\n';
}