#include <fstream>

using namespace std;

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

int main()
{
    int n,k;
    in>>n>>k;
    long long v[5000000],dq[5000000],s=0;
    int  st=0,dr=-1;
    for(int i=0; i<n; i++)
    {
        in>>v[i];
        if(i>=k && dq[st]==i-k)
        {
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]])
        {
            dr--;
        }
        dq[++dr]=i;
        if(i>=k-1)
            s+=v[dq[st]];
    }
    out<<s;
    return 0;
}