#include <iostream>
#include <fstream>
#include <vector>
#include <cstring>
#include <deque>
#define ll long long

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long n,i,j,v[5000005],S,k;
deque<int> dq;

int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++) f>>v[i];
    for(i=1;i<=k;i++)
    {
        while(!dq.empty() && v[dq.back()]>=v[i]) dq.pop_back();
        dq.push_back(i);
    }
    S+=v[dq.front()];
    for(i=k+1;i<=n;i++)
    {
        while(!dq.empty() && v[dq.back()]>=v[i]) dq.pop_back();
        dq.push_back(i);
        if(dq.front()<=(i-k)) dq.pop_front();
        S+=v[dq.front()];
    }
    g<<S<<'\n';
    return 0;
}