#include <fstream>
#include <deque>
using namespace std;

int64_t a[5000001];

int main(){

    ifstream cin("deque.in");
    ofstream cout("deque.out");
    deque < int > Dq;
    int n, k;
    cin >> n >> k;
    for(int i = 1; i <= k; ++i){
        cin >> a[i];
        while( ! Dq.empty() && a[Dq.back()] >= a[i])
            Dq.pop_back();
        Dq.push_back(i);
    }
    int64_t ans = a[Dq.front()];
    for(int i = k + 1; i <= n; ++i){
        cin >> a[i];
        while( ! Dq.empty() && a[Dq.back()] >= a[i])
            Dq.pop_back();
        Dq.push_back(i);
        if(Dq.front() == i - k)
            Dq.pop_front();
        ans += a[Dq.front()];
    }
    cout << ans;

    return 0;
}