#include <fstream>
#define nmax 5000001

using namespace std;

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

int n,k,v[nmax],d[nmax],st=1,dr;
long long sum;

inline void stanga(int i)
{
    if(i-d[st]==k)
        st++;
}

inline void dreapta(int i)
{
    while(st<=dr && v[i]<=v[d[dr]])
        dr--;
    d[++dr]=i;
}

int main()
{
    int i;
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
        stanga(i);
        dreapta(i);
        if(i>=k)
            sum+=v[d[st]];
    }
    fout<<sum;
    return 0;
}