#include <iostream>
#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,v[5000001];
long long s;
deque<int>q;
int main()
{
    fin>>n>>k;
    for(i=1; i<=n; i++)
    {
        fin>>v[i];
        while(!q.empty()&&v[q.back()]>v[i])
        {
            q.pop_back();
        }
        q.push_back(i);
        while(!q.empty()&&q.front()<i-k+1)
        {
            q.pop_front();
        }
        if(i>=k)s+=v[q.front()];
    }
    fout<<s;
    /*2 5 7 4 6 2

    4
    */
    return 0;
}