#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
list<pair<int,int> > Q;
int n,k,i,v;
long long sum;
int main()
{
    f>>n>>k;
    for(i=1; i<k; i++)
    {
        f>>v;
        while(Q.size()&&v<=Q.back().first)
            Q.pop_back();
        Q.push_back(make_pair(v,i));
    }
    for(; i<=n; i++)
    {
        f>>v;
        while(Q.size()&&v<=Q.back().first)
            Q.pop_back();
        Q.push_back(make_pair(v,i));
        sum+=Q.front().first;
        if(Q.front().second==i-k+1)
            Q.pop_front();

    }
    g<<sum;

    return 0;
}