#include <bits/stdc++.h>
using namespace std;
deque<pair<int, int>> dq;
int v[5000005];
int main(){
    ifstream cin ("deque.in");
    ofstream cout ("deque.out");
    int n, k;
    long long int sum=0;
    cin >> n >> k;
    for(int i=1; i<=n; i++)
        cin >> v[i];
    for(int i=1; i<=n; i++){
        while(!dq.empty() && dq.front().second<=i-k)
            dq.pop_front();
        while(!dq.empty() && dq.back().first>=v[i])
            dq.pop_back();
        dq.push_back({v[i], i});
        if(i>=k)
            sum+=dq.front().first;
    }
    cout << sum;
    return 0;
}