Cannot implicity convert type 'decimal' to 'int'. An explicit conversion exists (are you missing a cast?)

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C#

C#4.0

VS2012

First I want to say that I am very noob before you go bashing at how bad my code is, this is the first program I have ever written and I started learning just today. The error I have is on row 27

Also if I could ask another question in my current question. Where is the correct place to put global variables? As you see I put one inside form1 I think. I'm not sure where else to put. I am reading and watching some tutorials but not all my questions are answered. :/

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        int currentmana = 200;
        public Form1()
        {
            InitializeComponent();
        }

        
        private void button1_Click(object sender, EventArgs e)
        {
            if (currentmana >= manareq.Value && currentmana == manaactive.Value)
            {
                label1.Text = spell.Text;
                currentmana = currentmana - manareq.Value;
            }
            else if (currentmana != manareq.Value || manaactive.Value > currentmana)
            {
               MessageBox.Show("You don't have enough mana");
            }

        }
        
        private void timer1_Tick(object sender, EventArgs e)
        {
            label2.Text = (currentmana.ToString());

        }

        private void timer2_Tick(object sender, EventArgs e)
        {
            currentmana = 1 + currentmana;
        }
    }
}