#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k;
long long suma,x,curent=10000000;
deque<pair<int,int> > q;
int main()
{
    fin>>n>>k;
    for (int i=1;i<=n;i++)
    {
        fin>>x;
        while(!q.empty() && q.back().first>x)
            q.pop_back();
        q.push_back({x,i});
        while(!q.empty() && q.front().second<=i-k)
            q.pop_front();
        if (i>=k)
            suma+=q.front().first;
    }
    fout<<suma<<'\n';
    return 0;
}