#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int main(){
int a[5000001];
long long  n, k;
in >> n >> k;
for(long long  i = 0; i < n; i++){
    in >> a[i];
}
long long s = 0;
deque<long long>d;
for(int i = 0; i < n; i++){
    while(!d.empty() && d.front() <= i-k)
        d.pop_front();
    while(!d.empty() && a[d.back()] >= a[i])
        d.pop_back();
    d.push_back(i);

    if(i >= k-1)
        s += a[d.front()];
}
 out << s;
in.close();
out.close();
    return 0;
}