#include <iostream>
#include <fstream>
#include <deque>
/**L9 GANG LEADER
WHEN THE IMPOSTOR IS SUS?????? SOLOBOLO
*/
using namespace std;
string files="deque";
ifstream in(files+".in");
ofstream out(files+".out");
deque<int> dq;
int v[500001];
int main()
{
    int n,k;
    in>>n>>k;
    long long sol=0;
    for(int i=1;i<=n;i++)
    {
        in>>v[i];
        while(!dq.empty()&&v[dq.back()]>=v[i])
            dq.pop_back();
        dq.push_back(i);
        if(i-dq.front()>=k)
            dq.pop_front();
        if(i>=k)
            sol=sol+1LL*v[dq.front()];
    }
    out<<sol;
    return 0;
}