#include <iostream>
#include <fstream>
#include <deque>
#include <vector>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<int> q;
int v[5000001];
int main()
{long long n,k,i,s=0;
f>>n>>k;
for(i=1;i<=n;i++)
{
    f>>v[i];
    if(!q.empty())
    while(v[i]<=v[q.back()])
    q.pop_back();
    q.push_back(i);
    if(i>=k)
    {
        if(i-k==q.front())
        q.pop_front();
        s+=v[q.front()];
    }
}
g<<s;
    return 0;
}