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

int main()
{
    long n, k, x;
    long long s;
    deque<pair<int, int> > D; //position, value;
    ifstream in("deque.in");
    ofstream out("deque.out");
    in>>n>>k;
    for(long i=0; i<k; ++i)
    {
        in>>x;
        while(!D.empty()&&D.back().second>=x)
            D.pop_back();
        D.push_back(make_pair(i, x));
    }
    s=D.front().second;
    for(long i=k; i<n; ++i)
    {
        in>>x;
        if(D.front().first<=i-k)
            D.pop_front();
        while(!D.empty()&&D.back().second>=x)
            D.pop_back();
        D.push_back(make_pair(i, x));
        s+=D.front().second;
    }
    out<<s<<endl;
    in.close(); out.close();
    return 0;
}