contract TelMD is ERC20Interface, Ownable, MinterRole{
     using SafeMath for uint256;

     uint256 private _totalSupply;
     mapping(address => uint256) private _balances;
     mapping(address => mapping (address => uint256)) private _allowed;

     string public constant symbol = "TMD";
     string public constant name = "TelMD";
     uint public constant decimals = 18;
     
     constructor () public {
          _totalSupply = 500000000 * (10 ** decimals);
          _balances[msg.sender] = _totalSupply;
            
          emit Transfer(address(0), msg.sender, _totalSupply);
     }

     /**
     * @dev Total number of tokens in existence
     */
     function totalSupply() public view returns (uint256) {
          return _totalSupply;
     }

     /**
     * @dev Gets the balance of the specified address.
     * @param owner The address to query the balance of.
     * @return A uint256 representing the amount owned by the passed address.
     */
     function balanceOf(address owner) public view returns (uint256) {
          return _balances[owner];
     }

     /**
     * @dev Transfer token to a specified address
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     */
     function transfer(address to, uint256 value) public returns (bool) {
          _transfer(msg.sender, to, value);
          return true;
     }

     /**
     * @dev Function to mint tokens
     * @param to The address that will receive the minted tokens.
     * @param value The amount of tokens to mint.
     * @return A boolean that indicates if the operation was successful.
     */
     function mint(address to, uint256 value) public onlyMinter returns (bool) {
          _mint(to, value);
          return true;
     }

     /**
     * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
     * @param spender The address which will spend the funds.
     * @param value The amount of tokens to be spent.
     */
     function approve(address spender, uint256 value) public returns (bool) {
          _approve(msg.sender, spender, value);
          return true;
     }

     /**
     * @dev Transfer tokens from one address to another.
     * @param from address The address which you want to send tokens from
     * @param to address The address which you want to transfer to
     * @param value uint256 the amount of tokens to be transferred
     */
     function transferFrom(address from, address to, uint256 value) public returns (bool) {
          _transfer(from, to, value);
          _approve(from, msg.sender, _allowed[from][msg.sender].sub(value));
          return true;
     }

     /**
     * @dev Function to check the amount of tokens that an owner allowed to a spender.
     * @param owner address The address which owns the funds.
     * @param spender address The address which will spend the funds.
     * @return A uint256 specifying the amount of tokens still available for the spender.
     */
     function allowance(address owner, address spender) public view returns (uint256) {
          return _allowed[owner][spender];
     }

     /**
     * @dev Increase the amount of tokens that an owner allowed to a spender.
     * @param spender The address which will spend the funds.
     * @param addedValue The amount of tokens to increase the allowance by.
     */
     function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
          _approve(msg.sender, spender, _allowed[msg.sender][spender].add(addedValue));
          return true;
     }

     /**
     * @dev Decrease the amount of tokens that an owner allowed to a spender.
     * @param spender The address which will spend the funds.
     * @param subtractedValue The amount of tokens to decrease the allowance by.
     */
     function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
          _approve(msg.sender, spender, _allowed[msg.sender][spender].sub(subtractedValue));
          return true;
     }

     /**
     * @dev Transfer token for a specified addresses
     * @param from The address to transfer from.
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     */
     function _transfer(address from, address to, uint256 value) internal {
          require(to != address(0));

          _balances[from] = _balances[from].sub(value);
          _balances[to] = _balances[to].add(value);
          emit Transfer(from, to, value);
     }

     /**
     * @dev Internal function that mints an amount of the token and assigns it to
     * an account. This encapsulates the modification of balances such that the
     * proper events are emitted.
     * @param account The account that will receive the created tokens.
     * @param value The amount that will be created.
     */
     function _mint(address account, uint256 value) internal {
          require(account != address(0));
          
          _totalSupply = _totalSupply.add(value);
          _balances[account] = _balances[account].add(value);
          emit Transfer(address(0), account, value);
     }

     /**
     * @dev Approve an address to spend another addresses' tokens.
     * @param owner The address that owns the tokens.
     * @param spender The address that will spend the tokens.
     * @param value The number of tokens that can be spent.
     */
     function _approve(address owner, address spender, uint256 value) internal {
          require(spender != address(0));
          require(owner != address(0));

          _allowed[owner][spender] = value;
          emit Approval(owner, spender, value);
     }

     function () external payable {
          revert();
     }
}
function _transfer(address from, address to, uint256 value) internal {
     require(to != address(0));

     _balances[from] = _balances[from].sub(value);
     _balances[to] = _balances[to].add(value);
     emit Transfer(from, to, value);
}

/**
 * @dev Transfer token for a specified addresses
 * @param from The address to transfer from.
 * @param to The address to transfer to.
 * @param value The amount to be transferred.
 */