#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[5000001],d[5000001],st,dr=-1,k;
inline void stanga(int i)
{
    if(i-k==d[st])
        st++;
}
inline void dreapta(int i)
{
    while(st<=dr&&v[i]<=v[d[dr]])
        dr--;
    d[++dr]=i;
}
int main()
{
    int n,i,k,s=0;
    in>>n>>k;
    for(i=1; i<=n; i++)
    {
        in>>v[i];
        if(i>k){
        stanga(i);
        dreapta(i);}
        else
        stanga(i);
        s+=v[d[st]];
    }
    out<<s-1;
    return 0;
}