#include<bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<int>d;
long long s;
int n,m,a[5000001];
int main()
{
    f>>n>>m;
    for(int i=1;i<=n;++i)
        f>>a[i];
    d.push_back(1);
    for(int i=2;i<=n;++i)
    {
        while(!d.empty() && a[i]<a[d.back()])
            d.pop_back();
        d.push_back(i);
        if(i>=m)
        {if(i-d.front()==m)
            d.pop_front();
            s+=a[d.front()];
        }
    }
    g<<s;
}