atm.sol

pragma solidity ^0.4.16;

contract Atm {
    mapping(address => bool) public withdrawer;
    uint256 public basicAmount;
    address public owner;
    
    function Atm() public payable {
        owner = msg.sender;
    }
    
    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }
    
    function changeBaicAmount(uint256 newAmount) public onlyOwner {
        basicAmount = newAmount;
    }
    
    function withdraw() public payable returns(bool success) {
        require(!withdrawer[msg.sender]);
        require(address(this).balance > basicAmount);
        msg.sender.transfer(basicAmount);
        withdrawer[msg.sender] = true;
        return true;
    }
    
    function balance() public view returns(uint256) {
        return address(this).balance;
    }
}