#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

ifstream in ("deque.in");
ofstream out ("deque.out");

int a[5000005], n, k;
long long rez;
deque <int> q;

int main()
{
    in>>n>>k;
    for(int i = 1; i <= n; ++i){
        in>>a[i];
        while(!q.empty() && a[q.back()]>a[i])
            q.pop_back();
        q.push_back(i);
        if(i-q.front()+1>k)
            q.pop_front();
        if(i>=k)
            rez += 1ll*a[q.front()];
    }

    out<<rez;

    return 0;
}