#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

int n, d[5000001], v[5000001], st, dr, k;

long long s;

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

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

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