#include <fstream>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
#define NMAX 5000005
int deque[NMAX],k,st=1,dr,n,v[NMAX];
long long sum;
void read()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
        fin>>v[i];
}
void stanga(int poz)
{
    if(poz - deque[st] == k)
        st++;
}
void dreapta(int poz)
{
    while(st <= dr && v[poz] <= v[deque[dr]])
        dr--;
}
void solve()
{
    for(int i=1;i<=n;i++)
    {
        if(i>k) stanga(i);
        dreapta(i);
        deque[++dr] = i;
        if(i>=k) sum+= v[deque[st]];
    }
}
int main()
{
    read();
    solve();
    fout<<sum;
}