#include <fstream>
#include <deque>

using namespace std;

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

int v[5000000];
deque <int> d;

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