#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
#define cin fin
#define cout fout
#define int long long
const int NMAX = 5e6 + 5;
int n, k;
int v[NMAX];
deque<int> dq;
int min1[NMAX];

signed main(){
    cin >> n >> k;
    for (int i = 0; i < n; ++ i){
        cin >> v[i];
    }

    for (int i = 0; i < k; ++ i){
        while (!dq.empty() && v[dq.back()] > v[i]){
            dq.pop_back();
        }
        dq.push_back(i);
    }
    min1[0] = v[dq.front()];
    int sum = min1[0];
    for (int i = k; i < n; ++ i){
        if (dq.front() <= i - k){
            dq.pop_front();
        }
        while (!dq.empty() && v[dq.back()] > v[i]){
            dq.pop_back();
        }
        dq.push_back(i);
        min1[i - k + 1] = v[dq.front()];
        sum += min1[i - k + 1];
    }
    cout << sum;

    return 0;
}