uint256 constant private MAX_UINT256 = 2**256 - 1;
mapping (address => uint256) public balances;
mapping (address => mapping (address => uint256)) public allowed;
/*
NOTE:
The following variables are OPTIONAL vanities. One does not have to include them.
They allow one to customise the token contract & in no way influences the core functionality.
Some wallets/interfaces might not even bother to look at this information.
*/
string public name;                   //fancy name: eg Simon Bucks
uint8 public decimals;                //How many decimals to show.
string public symbol;                 //An identifier: eg SBX

function BERToken(
    uint256 _initialAmount,
    string _tokenName,
    uint8 _decimalUnits,
    string _tokenSymbol
) public {
    balances[msg.sender] = _initialAmount;               // Give the creator all initial tokens
    totalSupply = _initialAmount;                        // Update total supply
    name = _tokenName;                                   // Set the name for display purposes
    decimals = _decimalUnits;                            // Amount of decimals for display purposes
    symbol = _tokenSymbol;                               // Set the symbol for display purposes
}

function transfer(address _to, uint256 _value) public returns (bool success) {
    require(balances[msg.sender] >= _value);
    balances[msg.sender] -= _value;
    balances[_to] += _value;
    emit Transfer(msg.sender, _to, _value); //solhint-disable-line indent, no-unused-vars
    return true;
}

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
    uint256 allowance = allowed[_from][msg.sender];
    require(balances[_from] >= _value && allowance >= _value);
    balances[_to] += _value;
    balances[_from] -= _value;
    if (allowance < MAX_UINT256) {
        allowed[_from][msg.sender] -= _value;
    }
    emit Transfer(_from, _to, _value); //solhint-disable-line indent, no-unused-vars
    return true;
}

function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances[_owner];
}

function approve(address _spender, uint256 _value) public returns (bool success) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value); //solhint-disable-line indent, no-unused-vars
    return true;
}

function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
    return allowed[_owner][_spender];
}