#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
struct ura{
int nr,poz;
}v[500001];

int main()
{
    long long n,i,k,st=0,nr,dr=0,sum=0;
    cin>>n>>k;
    for(i=1;i<=n;i++){
        cin>>nr;

        if(v[st].poz+k-1<i &&st<=dr)
            st++;

        while(v[dr].nr>nr && dr>=st)
            dr--;

            dr++;
            v[dr].nr=nr;
            v[dr].poz=i;
        if(i>=k)
            sum+=v[st].nr;

    }
    cout<<sum;
    return 0;
}