#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long int n,k,a[5000001],stiva[5000001],suma=0,stanga=1,dreapta=1,i;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>a[i];
    for(i=1;i<=n;i++)
    {
        while(dreapta>=stanga && a[stiva[dreapta]]>a[i])
            dreapta--;
        if(dreapta>=stanga && stiva[stanga]==i-k)
            stanga++;
        stiva[++dreapta]=i;
        if(i>=k)
            suma=suma+a[stiva[stanga]];
    }
    g<<suma;
    f.close();
    g.close();
    return 0;
}