pragma solidity >=0.4.22 <0.6.0;
contract tokens {

    address owner;
    uint256 rate;
    mapping (address => uint256) token;
    uint256 totalBalance;

    constructor(uint256 x) public
    {
        if (x==0)
        {
            x = 1;
        }
        rate = x;
        owner = msg.sender;
    }

    function () external payable
    {
        token[msg.sender] += msg.value * rate;
        totalBalance += msg.value * rate;
    }

    function showBalance(address tokenOwner) public returns (uint256)
    {
        return token[tokenOwner];
    }

    function changeRate(uint256 x) public
    {
        require (msg.sender == owner);
        if (x==0)
        {
            x = 1;
        }
        rate = x;
    }

    function getMoney() public
    {
        require (msg.sender == owner);
        (msg.sender).transfer(totalBalance);
        totalBalance = 0;
    }

    function totalSupply() public view returns (uint)
    {
        return totalBalance;
    }

    function balanceOf(address tokenOwner) public view returns (uint)
    {
        return token[tokenOwner];
    }

    function transferFrom(address from, address to, uint amount) public returns (bool success)
    {
        require(msg.sender == from);
        if (token[from] < amount)
        {
            return false;
        }
        else
        {
            token[to] += amount;
            token[from] -= amount;
        }
    }


}