#include <bits/stdc++.h>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");
int n, k, i, a[5000001];
deque<int> deq;
long long s;

int main() {
    f>>n>>k;
    for(i=1;i<k;i++) {
        f>>a[i];
        deq.push_back(i);
    }
    for(i=k;i<=n;i++) {
        f>>a[i];
        while(!deq.empty() && a[deq.back()]>a[i])deq.pop_back();
        deq.push_back(i);
        if(i-deq.front()>=k)deq.pop_front();
        s+=a[deq.front()];
    }
    g<<s;
    return 0;
}