#include <fstream>
#include <vector>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int n, k;
vector <int> v;
deque <int> dq;
int main()
{
    cin>>n>>k;
    for(int i=0;i<n;i++)
    {
        int x;  cin>>x;
        v.push_back(x);
    }
    long long int sum=0;
    for(int i=0;i<n;i++)
    {
        while(!dq.empty() && v[dq.back()]>=v[i])
            dq.pop_back();
        dq.push_back(i);
        if(i<k-1)
            continue;
        while(dq.front()<=i-k)
            dq.pop_front();
        sum+=v[dq.front()];
    }
    cout<<sum;

    return 0;
}