#include <fstream>
#include <deque>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

const int N=5000005;

int n, k, v[N];
long long sol;

int main()
{
    fin>>n>>k;
    deque<int> q;
    for(int i=0;i<n;++i)
    {
        fin>>v[i];
        while(q.size()&&v[q.back()]>=v[i])
            q.pop_back();
        q.push_back(i);
        if(q.front()<=i-k)
            q.pop_front();
        if(i>=k-1)
            sol+=v[q.front()];
    }
    fout<<sol;
    return 0;
}