#include <bits/stdc++.h>
using namespace std;
int a[5000003];
int main()
{
    int n,k,i,x;
    int64_t s=0;
    ifstream f("deque.in");
    f>>n>>k;
    for(i=1; i<=n; i++)
        f>>a[i];
    deque<int>q;
    for(i=1; i<=k; i++)
    {
        x=a[i];
        while(!q.empty() && x<= a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    s+=a[q.front()];
    for(i=k+1; i<=n; i++)
    {
        x=a[i];
        while(!q.empty() && x<= a[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i-q.front() >= k)
            q.pop_front();
        s+=a[q.front()];
    }
    cout<<s;
    return 0;
}