#include <fstream>
#include <deque>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque <int> st;
int n,k,x,v[5000005],i;
long long S;
int main()
{
    cin>>n >>k;
    for(i=1;i<=n;i++){
        cin>>v[i];
        while(!st.empty() && st.back()<=i-k)st.pop_back();
        while(!st.empty() && v[i]<v[st.front()])st.pop_front();
        st.push_front(i);
        if(i>=k)S+=v[st.back()];
    }
    cout<<S;
}