#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,v[5000009];
long long sum;
deque<int>dq;
int main()
{
    f>>n>>k;
    for(int i=1; i<=n; i++)
    {
        f>>v[i];
        while(!dq.empty()&&v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front()==i-k)
            dq.pop_front();
        if(i>=k)sum+=v[dq.front()];
    }
    g<<sum;
    return 0;
}