#include <fstream>
#include <deque>

using namespace std;

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

int v[5000001];

deque<int>dq;

int main()
{
    long long n,k,i,s;
    cin>>n>>k;
    for(i=1;i<=n;i++)
        cin>>v[i];
    s=0;
    for(i=1;i<=n;i++){
        while(dq.empty()==0 && v[dq.back()]>v[i])
            dq.pop_back();
        while(dq.empty()==0 && dq.front()<=i-k)
            dq.pop_front();
        dq.push_back(i);
        if(i>=k)
           s=s+v[dq.front()];
    }
    cout<<s;
    return 0;
}