#include <iostream>
#include <fstream>
#include <deque>
#define int long long
using namespace std;

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

const int Nmax=5e6;
int V[Nmax+3],n,k;
deque < pair<int,int> > Q;
int S=0;

int32_t main()
{
    f >> n >> k;
    for(int i=1; i<=n; i++)
        f >> V[i];
    for(int i=1; i<=k; i++)
    {
        while(Q.size() && Q.back().first>=V[i])
            Q.pop_back();
        Q.push_back(make_pair(V[i],i));
    }
    S+=Q.front().first;
    for(int i=k+1; i<=n; i++)
    {
        while(Q.size() && Q.back().first >= V[i])
            Q.pop_back();
        Q.push_back(make_pair(V[i],i));
        if(Q.front().second<i-k+1)
            Q.pop_front();
        S+=Q.front().first;
    }
    g << S;
    return 0;
}