#include <iostream>
#include <fstream>
#define size 5000000

using namespace std;

int v[size], dq[size];

int main () {
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    int n, k, st, dr, s;

    fin>>n>>k;
    st = 0; dr = -1; s = 0;
    for ( int i = 0; i < n; i++ ) {
        fin>>v[i];
        //scot din st
        if ( st <= dr && dq[st] == i - k )
            st++;
        //scot din dr
        while ( st <= dr && v[i] <= v[dq[dr]] )
            dr--;
        //adaug i
        dq[++dr] = i;
        //actualizez rez global
        if ( i >= k - 1 )
            s += v[dq[st]];
    }

    fout<<s;
    return 0;
}