pragma solidity >=0.4.22 <0.6.0;

contract SafeMath {
    function safeMul(uint256 a, uint256 b) public pure  returns (uint256)  {
        uint256 c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }

    function safeDiv(uint256 a, uint256 b)public pure returns (uint256) {
        assert(b > 0);
        uint256 c = a / b;
        assert(a == b * c + a % b);
        return c;
    }

    function safeSub(uint256 a, uint256 b)public pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    function safeAdd(uint256 a, uint256 b)public pure returns (uint256) {
        uint256 c = a + b;
        assert(c>=a && c>=b);
        return c;
    }

    function _assert(bool assertion)public pure {
      assert(!assertion);
    }
}


contract ERC20Interface {
    string public name;
    string public symbol;
    uint8 public  decimals;
    uint public totalSupply;
    
    function transfer(address _to, uint256 _value) public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
    function approve(address _spender, uint256 _value) public returns (bool success);
    function allowance(address _owner, address _spender)public view returns (uint256 remaining);
    
    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
 }
 
contract ERC20 is ERC20Interface,SafeMath {
    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) allowed;

    constructor(string memory _name) public {
        name = _name;
        symbol = "GSD";
        decimals = 6;
        totalSupply = 990000000000;
        balanceOf[msg.sender] = totalSupply;
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
        require(_to != address(0));
        require(balanceOf[msg.sender] >= _value);
        require(balanceOf[ _to] + _value >= balanceOf[ _to]);  

        balanceOf[msg.sender] =SafeMath.safeSub(balanceOf[msg.sender],_value) ;
        balanceOf[_to] =SafeMath.safeAdd(balanceOf[_to] ,_value);

   
        emit Transfer(msg.sender, _to, _value);
 
        return true;
    }


    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_to != address(0));
        require(allowed[_from][msg.sender] >= _value);
        require(balanceOf[_from] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);

        balanceOf[_from] =SafeMath.safeSub(balanceOf[_from],_value) ;
        balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to],_value);

        allowed[_from][msg.sender] =SafeMath.safeSub(allowed[_from][msg.sender], _value);

        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool success) {
        require((_value==0)||(allowed[msg.sender][_spender]==0));
        allowed[msg.sender][_spender] = _value;
 
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
      
        return allowed[_owner][_spender];
    }

}


contract owned {
    address public owner;

    constructor () public {
        
        owner = msg.sender;
    }

    modifier onlyOwner {
        
        require(msg.sender == owner);
        _;
    }

    function transferOwnerShip(address newOwer) public onlyOwner {
        
        owner = newOwer;
    }

}

contract GSD is ERC20,owned{
    mapping (address => bool) public frozenAccount;

    event FrozenFunds(address target, bool frozen);
    event Burn(address target, uint amount);

    constructor (string memory _name) ERC20(_name) public {

    }


    function freezeAccount(address target, bool freeze) public onlyOwner {
        
        frozenAccount[target] = freeze;
        emit FrozenFunds(target, freeze);
    }


    function transfer(address _to, uint256 _value) public returns (bool success) {
        
        success = _transfer(msg.sender, _to, _value);
    }


    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(allowed[_from][msg.sender] >= _value);
        require(!frozenAccount[msg.sender]);
        require(!frozenAccount[_from]);
	    require(!frozenAccount[_to]);
        
        success =  _transfer(_from, _to, _value);
        allowed[_from][msg.sender] =SafeMath.safeSub(allowed[_from][msg.sender],_value) ;
    }

    function _transfer(address _from, address _to, uint256 _value) internal returns (bool success) {
        require(_to != address(0));
        require(!frozenAccount[_from]);
        require(!frozenAccount[_to]);

        require(balanceOf[_from] >= _value);
        require(balanceOf[ _to] + _value >= balanceOf[ _to]);

        balanceOf[_from] =SafeMath.safeSub(balanceOf[_from],_value) ;
        balanceOf[_to] =SafeMath.safeAdd(balanceOf[_to],_value) ;

        emit Transfer(_from, _to, _value);
        return true;
    }

    function burn(uint256 _value) public returns (bool success) {
        require(owner == msg.sender);
        require(balanceOf[msg.sender] >= _value);

        totalSupply =SafeMath.safeSub(totalSupply,_value) ;
        balanceOf[msg.sender] =SafeMath.safeSub(balanceOf[msg.sender],_value) ;

        emit Burn(msg.sender, _value);
        return true;
    }

    function burnFrom(address _from, uint256 _value)  public returns (bool success) {
        require(owner == msg.sender);
        require(balanceOf[_from] >= _value);
        require(allowed[_from][msg.sender] >= _value);

        totalSupply =SafeMath.safeSub(totalSupply,_value) ;
        balanceOf[_from] =SafeMath.safeSub(balanceOf[_from], _value);
        allowed[_from][msg.sender] =SafeMath.safeSub(allowed[_from][msg.sender],_value);

        emit Burn(_from, _value);
        return true;
    }
}