#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int n,k;
long long sol;
deque <pair<long long,int>> dq;

int main()
{   f>>n>>k;
    for(int i=1; i<=k; i++)
    {   long long x;
        f>>x;
        if(dq.empty())
            dq.push_back(make_pair(x,i));
        else
        {   while(!dq.empty() && dq.back().first>x)
                dq.pop_back();
            dq.push_back(make_pair(x,i));
        }
    }
    sol+=dq.front().first;
    for(int i=k+1; i<=n; i++)
    {   long long x;
        f>>x;
        if(dq.front().second<=i-k)
            dq.pop_front();
        if(dq.empty())
            dq.push_back(make_pair(x,i));
        else
        {   while(!dq.empty() && dq.back().first>x)
                dq.pop_back();
            dq.push_back(make_pair(x,i));
        }
        sol+=dq.front().first;
    }
    g<<sol;
    g.close(); return 0;
}