#include <bits/stdc++.h>
#define oo 5000005
using namespace std;

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

int n, k , v[oo];
long long int sum;

deque < int > d;

int main(){
    in>>n>>k;
    for(int i = 1; i <= n; i++){
        in>>v[i];
        while(!d.empty() && v[i] <= v[d.back()])
            d.pop_back();
        d.push_back(i);

        if(d.front() == i - k)
            d.pop_front();
        if(i >= k)
            sum += v[d.front()];
    }
    out<<sum;
}