#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int d[500000], k, i, a[5000001],dr,st,n;
long long s;
inline void stanga()
{
    if(d[st]==i-k) st++;
}
inline void dreapta()
{
    while(st<=dr&&a[i]<=a[d[dr]])
    dr--;
}
int main()
{
    in>>n>>k;
    st=1; dr=0;
    s=0;
    for(i=1;i<=n;i++)
    {
        in>>a[i];
    }
    for(i=1;i<=n;i++)
    {
        if(i>k) stanga();
        dreapta();
        dr++;
        d[dr]=i;
        if(i>=k) s=s+a[d[st]];
    }
    out<<s;
    return 0;
}