#include <iostream>
#include <deque>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000000], n;
int main()
{
    int i, k;
    long long s=0;
    fin>>n>>k;
    for(i=1; i<=n; ++i)
        fin>>v[i];
    deque <int> d;
    for(i=1; i<=n; ++i)
    {
        while(!d.empty()&&v[d.back()]>=v[i])
            d.pop_back();
        d.push_back(i);
        if(i-k==d.front()) d.pop_front();
        if(i>=k) s+=v[d.front()];
    }
    fout<<s;
    return 0;
}