#include <iostream>
#include <deque>
#include <fstream>
using namespace std;

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

deque<int> DQ;

const int NMAX=5000001;

int v[NMAX];
long long sum=0;

int main()
{
    register int i,n,k;
    in>>n>>k;
    for(i=1; i<=n; i++)
    {
        in>>v[i];
    }
    for(i=1; i<k; i++)
    {
        while(DQ.empty()==0 && v[DQ.back()]>v[i])
        {
            DQ.pop_back();
        }
        DQ.push_back(i);
    }

    for(i=k; i<=n; i++)
    {
        while(DQ.empty()==0 && v[DQ.back()]>v[i])
        {
            DQ.pop_back();
        }
        DQ.push_back(i);
        if(DQ.front()<=i-k)
        {
            DQ.pop_front();
        }
        sum+=v[DQ.front()];
    }

    out<<sum;


}