#include<bits/stdc++.h>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque<int> d;
long long n,k,a[5000001],s;
int main()
{in>>n>>k;
for(int i=1;i<=n;i++)
    {in>>a[i];
    while(!d.empty() && a[i]<=a[d.back()])
        d.pop_back();
    d.push_back(i);
    if(d.front()==i-k) d.pop_front();
    if(i>=k) s+=a[d.front()];
    }
out<<s;
return 0;
}