stock GetSpeed(playerid)
{
    new
       vehicle = GetPlayerVehicleID(playerid),
       Float:speed_x,Float:speed_y,Float:speed_z,Float:Brzina;
    GetVehicleVelocity(vehicle,speed_x,speed_y,speed_z);
    Brzina = floatsqroot(((speed_x*speed_x)+(speed_y*speed_y))+(speed_z*speed_z))*176.666667;
    return floatround(Brzina,floatround_round);
}

public OnPlayerEnterCheckpoint(playerid)
{
    new brzina = GetSpeed(GetPlayerVehicleID(playerid));
    if(CP[playerid] == 1) // PREUZIMANJE
    {
       if(brzina >= 35) return GameTextForPlayer(playerid, "~r~SLOW DOWN!", 2500, 3);
           // rest of code
    }
    return (true);
}