#include <fstream>
#include <deque>

using namespace std;

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

deque < long long > a;

int main()
{
    long long n, k, i;
    long long x, s = 0;
    long long v[500001];

    fin >> n >> k;
    for ( i = 1 ; i <= n ; i++ ) fin >> v[i];

    for ( i = 1 ; i < k ; i++ )
    {
        x = v[i];
        if ( a.empty() == 0 ) while ( x <= a.back() || a.empty() != 0 ) a.pop_back();
        a.push_back ( x );
    }

    for ( i = k ; i <= n ; i++ )
    {
        x = v[i];
        while ( x <= a.back() ) a.pop_back();
        a.push_back ( x );

        if ( a.front() == v[i-k] ) a.pop_front();

        s += a.front();
    }

    fout << s;

    return 0;
}