#include <fstream>
#include <deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

long long i,N,K,sum=0,x;

deque < pair<long long, long long> > deq;

int main()
{
    f >> N;
    f >> K;

    for (i=0; i<N; ++i )
    {
        f >> x;
        while ( !deq.empty() && deq.back().first >= x )
            deq.pop_back();

        deq.push_back( make_pair(x, i) );

        if ( deq.front().second <= i-K )
            deq.pop_front();

        if (i >= K-1)
            sum += deq.front().first;
    }
    g << sum;
}