// File: /mnt/c/pr0/blockchain-developer-bootcamp/src/contracts/Token.sol



pragma solidity ^0.5.0;

import "openzeppelin-solidity/contracts/math/SafeMath.sol";

contract Token {
  using SafeMath for uint;

  // Variables
  string public name = "Sayvland Index";
  string public symbol = "SLI";
  uint256 public decimals = 18;
  uint256 public totalSupply;
  mapping(address => uint256) public balanceOf;
  mapping(address => mapping(address => uint256)) public allowance;

  // Events
  event Transfer(address indexed from, address indexed to, uint256 value);
  event Approval(address indexed owner, address indexed spender, uint256 value);

  constructor() public {
    totalSupply = 5000000000 * (10 ** decimals);
    balanceOf[msg.sender] = totalSupply;
  }

  function transfer(address _to, uint256 _value) public returns (bool success) {
    require(balanceOf[msg.sender] >= _value);
    _transfer(msg.sender, _to, _value);
    return true;
  }

  function _transfer(address _from, address _to, uint256 _value) internal {
    require(_to != address(0));
    balanceOf[_from] = balanceOf[_from].sub(_value);
    balanceOf[_to] = balanceOf[_to].add(_value);
    emit Transfer(_from, _to, _value);
  }

  function approve(address _spender, uint256 _value) public returns (bool success) {
    require(_spender != address(0));
    allowance[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
    require(_value <= balanceOf[_from]);
    require(_value <= allowance[_from][msg.sender]);
    allowance[_from][msg.sender] = allowance[_from][msg.sender].sub(_value);
    _transfer(_from, _to, _value);
    return true;
  }
}

// File: openzeppelin-solidity/contracts/math/SafeMath.sol



pragma solidity ^0.5.0;

/**
 * @title SafeMath
 * @dev Unsigned math operations with safety checks that revert on error
 */
library SafeMath {
    /**
    * @dev Multiplies two unsigned integers, reverts on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b);

        return c;
    }

    /**
    * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
    * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
    * @dev Adds two unsigned integers, reverts on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }

    /**
    * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
    * reverts when dividing by zero.
    */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }
}