#include <bits/stdc++.h>

using namespace std;

deque <int> qi;
deque <long long int> qn;

int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    long long int sum=0,x,n,k;
    cin>>n>>k;
    for(int i=1;i<=n;++i)
    {
        cin>>x;
        while(qi.size()>0 && qi.front()<(i-k+1))
        {
            qi.pop_front();
            qn.pop_front();
        }
        while(qn.size()>0 && qn.back()>=x)
        {
            qi.pop_back();
            qn.pop_back();
        }
        qi.push_back(i);
        qn.push_back(x);
        if(i>=k)
        {


        sum+=qn.front();
        }
    }
    cout<<sum;
    return 0;
}