#include<bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<int,int>> q;

int main()
{
    int n,i,j,k,nr,suma = 0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>nr;
        while(!q.empty() && q.back().first >= nr)
        {
            q.pop_back();
        }
        q.push_back({nr, i});
        if(i >= k)
            suma += q.front().first;
        if(i >= q.front().second + k - 1){
            q.pop_front();
        }
    }
    fout<<suma;
    return 0;
}