#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

#define MAX 5000020

deque < int > q;
int a[MAX];

int main()
{
    long long n,k,i,s=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];


    for(i=1;i<=n;i++){
        if(!q.empty() && q.front()==i-k)
            q.pop_front();
        while(!q.empty() && a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i>=k)
            s+=a[q.front()];
    }
    fout<<s<<endl;
    fin.close();
    fout.close();
    return 0;
}