#include <fstream>

using namespace std;

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

int v[5000001],d[5000001];

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