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

long long int sum, n, k, i, v[5000001];
deque <int> d;
ifstream f("deque.in");
ofstream g("deque.out");

int main()
{f>>n>>k;
for(i=1; i<=n; ++i) f>>v[i];
for(i=1; i<=n; ++i)
{
    while(d.size() && v[i]<=v[d.back()]) d.pop_back();
    d.push_back(i);
    if(d.front()==(i-k)) d.pop_front();
    if(i>=k) sum=sum+v[d.front()];
}
g<<sum;
g.close();
f.close();
return 0;
}