#include <fstream>
#include <deque>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
long long n, k, sum;
long long v[5000002];
deque<int>dq;
signed main() {
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        cin>>v[i];
    }
    for(int i=1;i<k;i++){
        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
    }
    for(int i=k;i<=n;i++){
        while(!dq.empty() && v[dq.back()]>v[i]){
            dq.pop_back();
        }
        dq.push_back(i);
        if(i-dq.front()>=k)
            dq.pop_front();
        sum+=v[dq.front()];
    }
    cout<<sum;
}