#include <bits/stdc++.h>
using namespace std;

const int NMAX = 5e6;

deque<int> q;
queue<int> coada;

int main() {
    FILE *fin, *fout;
    fin = fopen("deque.in", "r");
    fout = fopen("deque.out", "w");
    int n, k;
    fscanf(fin, "%d%d", &n, &k);
    long long ans = 0;
    for(int i = 0; i < k; i++) {
        int x;
        fscanf(fin, "%d", &x);
        coada.push(x);
        while(!q.empty() && x < q.back())
            q.pop_back();
        q.push_back(x);
    }
    //cout << q.front() << endl;
    ans += q.front();
    for(int i = k; i < n; i++) {
        //cout << "HATZ" << ' ' << q.front() << endl;
        if(q.front() == coada.front())
            q.pop_front();
        coada.pop();
        int x;
        fscanf(fin, "%d", &x);
        coada.push(x);
        while(!q.empty() && x < q.back())
            q.pop_back();
        q.push_back(x);
        //cout << q.front() << endl;
        ans += q.front();
    }
    fprintf(fout, "%lld", ans);
    fclose(fin);
    fclose(fout);
    return 0;
}