#include <fstream>
#include <deque>

using namespace std;

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

deque < int > d;
int v[5000001];

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