#include <iostream>
#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long i,n,k,v[5000010];
long long suma=0;
deque <long long> my_deq;
int main()
{
    f>>n>>k;
    for(i=0;i<n;i++)
    {
        f>>v[i];
        while (my_deq.size() && v[my_deq.back()]>=v[i])
            my_deq.pop_back();
        my_deq.push_back(i);
        if(my_deq.front()==i-k)
            my_deq.pop_front();
        if(i>=k-1)
            suma +=v[my_deq.front()];
    }
    g<<suma;
    return 0;
}