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

const int NMAX=5000005;

using namespace std;

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

int n,k;
long long v[NMAX];
long long s=0;
deque<int>val;

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