// Vulnerability label: FE1
pragma solidity ^0.5.17;

library SafeMath {
  function safeMul(uint256 a, uint256 b) internal  pure returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function safeDiv(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b > 0);
    uint256 c = a / b;
    assert(a == b * c + a % b);
    return c;
  }

  function safeSub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function safeAdd(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c>=a && c>=b);
    return c;
  }
}
contract Niubi {
    using SafeMath for uint256;
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;
	address public owner;

    mapping (address => uint256) public balanceOf;
	mapping (address => uint256) public freezeOf;
    mapping (address => mapping (address => uint256)) public allowance;

    event Transfer(address indexed from, address indexed to, uint256 value);

    event Burn(address indexed from, uint256 value);
    event Freeze(address indexed from, uint256 value);
    event Unfreeze(address indexed from, uint256 value);

    constructor() public {
        uint256 initialSupply=100000000000000*1e18;
        balanceOf[msg.sender] = initialSupply;             
        totalSupply = initialSupply;                    
        name = 'NIUB';                                
        symbol = 'NIUB';                              
        decimals = 18;                           
		owner = msg.sender;
    }


    function transfer(address _to, uint256 _value) public {
        require(_to!=address(0x0));                  
        require(_value > 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);                 
    }


    function approve(address _spender, uint256 _value) public
        returns (bool success) {
		require(_value>0);
        allowance[msg.sender][_spender] = _value;
        return true;
    }
       

  
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
         require(_to!=address(0x0));       
      	require(_value>0);
      	
	    require(balanceOf[_from] >= _value);
	    require(balanceOf[_to] + _value >= balanceOf[_to]);
	    require(_value <= allowance[_from][msg.sender]);
        balanceOf[_from] = SafeMath.safeSub(balanceOf[_from], _value);                          
        balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to], _value);                            
        allowance[_from][msg.sender] = SafeMath.safeSub(allowance[_from][msg.sender], _value);
        emit Transfer(_from, _to, _value);
        return true;
    }

    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);
        require(_value > 0);
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                     
        totalSupply = SafeMath.safeSub(totalSupply,_value);                               
        emit Burn(msg.sender, _value);
        return true;
    }
	
	function freeze(uint256 _value) public returns (bool success) {
	    require(balanceOf[msg.sender] >= _value);
	    require(_value > 0);
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                      
        freezeOf[msg.sender] = SafeMath.safeAdd(freezeOf[msg.sender], _value);                               
        emit Freeze(msg.sender, _value);
        return true;
    }
	
	function unfreeze(uint256 _value) public returns (bool success) {
	    require(freezeOf[msg.sender] >= _value);
	    require(_value>0);
        freezeOf[msg.sender] = SafeMath.safeSub(freezeOf[msg.sender], _value);                     
		balanceOf[msg.sender] = SafeMath.safeAdd(balanceOf[msg.sender], _value);
        emit Unfreeze(msg.sender, _value);
        return true;
    }
	

	function() external payable {
    }
}