#include <fstream>

using namespace std;

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

int b[5000001], k, i, a[5000001],dr,st(1),n;
long long s(0);

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

inline void dreapta(int i)
{
    while(st<=dr && a[i]<=a[b[dr]])
    dr--;
}
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>a[i];
    }
    for(i=1;i<=n;i++)
    {
        if(i>k) stanga(i);
        dreapta(i);
        dr++;
        b[dr]=i;
        if(i>=k) s+=a[b[st]];
    }
    fout<<s;
    return 0;
}