#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<int,int>> dq;

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