PHP-Mysql -data insert problem

insert data using mysqli-student data

<div id="submit"><h3>Student Data</h3>

<form method="post" action="input.php">
<label>student name:
<input type="text" name="name" id ="name" required="required" placeholder="Please Enter Name"/>
<p><br />


<label>student Last name:
<input type="text" name="Lname" id ="Lname" required="required" placeholder="Please Last Name"/><p><br />


<label>student Age:
<input type="text" name="age" id ="age" required="required" placeholder="Enter student Age"/>
<p><br />

<label>student DOB:
<input type="date" name="date" id ="date" required="required" placeholder="Enter student DOB"/>
<p><br />

<label>student sex:
<select id="sex" name="sex">

                    <option value="1">male</option>
                    <option value="2">female</option>
</select>
<p><br />

<label>student mark(out of 500):
<input type="text" name="mark" id ="mark" required="required" placeholder="Please Enter Mark"/><p><br />

<label>student mark(% of mark):
<input type="text" name="pmark" id ="pmark" required="required" placeholder="percentage"/><p><br />

<label>student place:
<input type="text" name="place" id ="place" required="required" placeholder="Enter student place"/>
<p><br />


<input type="submit" name="submit" value="sent"
<br />
</form></p></p></p></p></p></p></p></p></div>

// create connection

$conn= mysqli_connect ('localhost','root','','mydb');

if(mysqli_connect_errno())
{ 
echo" failed to conncet:" .mysqli_connect_errno();
}


$sql= "INSERT INTO mydb(name, Lname,age,date,sex,mark,pmark,place) 
VALUES ('$_POST[name]','$_POST[Lname]','$_POST[age]','$_POST[date]','$_POST[sex]','$_POST[mark]','$_POST[pmark]','$_POST[place]')";

if(!mysqli_query($conn,$sql))

{
 die('Error:'.mysqli_error($conn));

}
echo "1 record added"


?>