#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,a[5000010],c[5000010],inc,sf,i;
long long sum;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
        inc=1;
        sf=0;
    }
    for(i=1;i<=n;i++)
    {
        while(inc<=sf&&a[i]<=a[c[sf]])
        sf--;
        c[++sf]=i;
        if(c[inc]==i-k)
        inc++;
        if(i>=k)
        sum+=a[c[inc]];
    }
    g<<sum;
    return 0;
}