#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, i, a[5000002];
deque<int> q;
long long r;

int main() {
    fin >> n >> k;
    for(i = 1; i < k; i++) {
        fin >> a[i];
        while(!q.empty() && a[q.back()] >= a[i]) q.pop_back();
        q.push_back(i);
    }
    for(i = k; i <= n; i++) {
        fin >> a[i];
        while(!q.empty() && a[q.back()] >= a[i]) q.pop_back();
        q.push_back(i);

        if(!q.empty() && i - q.front() >= k) q.pop_front();
        r += a[q.front()];
    }
    fout << r;

    return 0;
}