#include <fstream>
#include <deque>
#define int long long
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int v[5000000];
deque<int> dq;
int32_t main() {
    int n,k;
    cin>>n>>k;
    for (int i=0; i<n; ++i) {
        cin>>v[i];
    }
    int sum=0;
    for (int i=0; i<n; ++i) {
        if (!dq.empty() && dq.front()==i-k) dq.pop_front();
        while (!dq.empty() && v[i]<v[dq.back()]) dq.pop_back();
        dq.push_back(i);
        if (i>=k-1) sum+=v[dq.front()];
    }
    cout<<sum;
}