#include <deque>
#include <iostream>
#include <fstream>

using namespace std;

#define nmax 5000000

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

int v[nmax], deq[nmax], n, k, st, dr;

int main()
{
    long long s = 0;
    f >> n >> k;
    for( int i = 0; i < n; ++i )
        f >> v[i];
    deq[dr] = v[0];
    for( int i = 1; i < k - 1; ++i )
    {
        for( ; v[i] < deq[dr] && dr >= st; --dr );
        deq[++dr] = v[i];
    }
    for( int i = k - 1; i < n; ++i )
    {
        for( ; v[i] < deq[dr] && dr >= st; --dr );
        deq[++dr] = v[i];
        s += deq[st];
        if( v[i - k + 1] == deq[st] )
            ++st;
    }
    g << s;
    f.close();
    g.close();
    return 0;
}