pragma solidity ^0.5.0;
contract MyToken{

    uint totalsupply;
    mapping (address => uint) tokenOwners;
    address owner;
    uint sellingRate;
    uint eth;

    constructor (uint _sellingRate) public{
        owner = msg.sender;
        if (_sellingRate == 0)
        {
            sellingRate = 1;
        }
        else
        {
            sellingRate = _sellingRate;
        }
    }

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

    function changeRate(uint _sellingRate) public {
        require(msg.sender == owner);
        if (_sellingRate != 0)
            sellingRate = _sellingRate;
        else
            sellingRate = 1;
    }

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

    function transfer(address to, uint tokens) public returns (bool success){
        if (tokenOwners[msg.sender] >= tokens){
            tokenOwners[msg.sender] -= tokens;
            tokenOwners[to] += tokens;
            emit Transfer(msg.sender, to, tokens);
            return true;
        }
        else{
            return false;
        }
    }

    function () external payable{
        totalsupply += msg.value / sellingRate;
        tokenOwners[msg.sender] =  msg.value / sellingRate;
        eth += msg.value;
    }

    function getETH() public{
        require(msg.sender == owner);
        (msg.sender).transfer(eth);
        eth = 0;
    }

    event Transfer(address indexed from, address indexed to, uint tokens);
}