#include <bits/stdc++.h>
using namespace std;
deque<int> q;
long long v[5000005];

int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n, k;
    long long s=0;
    cin>>n>>k;
    for(int i=1; i<=n; i++)
        cin>>v[i];
    for(int i=1; i<=n; i++)
    {
        while(q.empty()==false && v[i]<v[q.back()])
            q.pop_back();
        if(q.empty()==false && q.front()<=i-k)
            q.pop_front();
        q.push_back(i);
        if(i>=k)
            s+=v[q.front()];
    }
    cout<<s;

    return 0;
}