#include <fstream>

using namespace std;

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

int c[5000001],v[5000001];

int main()
{
    int n,i,sf=0,inc=0,k;
    long long s=0;
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>v[i];
        if(i<k)
        {
            while(sf>=inc && v[i]<v[c[sf]])
                sf--;
            sf++;
            c[sf]=i;
        }
        else
        {
            if(i-k+1>c[inc])
                inc++;
            while(sf>=inc && v[i]<v[c[sf]])
                sf--;
            sf++;
            c[sf]=i;
            s+=v[c[inc]];
        }
    }
    cout<<s;
    return 0;
}