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

using namespace std;

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

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