pragma solidity ^0.8.18;

//Safe Math Interface
abstract contract SafeMath {
    function safeAdd(uint a, uint b) public pure virtual returns (uint c) {
        c = a + b;
        require(c >= a, "SafeMath: addition overflow");
    }
    
    function safeSub(uint a, uint b) public pure virtual returns (uint c) {
        require(b <= a, "SafeMath: subtraction overflow");
        c = a - b;
    }
    
    function safeMul(uint a, uint b) public pure virtual returns (uint c) {
        c = a * b;
        require(a == 0 || c / a == b, "SafeMath: multiplication overflow");
    }
    
    function safeDiv(uint a, uint b) public pure virtual returns (uint c) {
        require(b > 0, "SafeMath: division by zero");
        c = a / b;
    }
}

//ERC Token Standard #20 Interface
abstract contract ERC20Interface {
    function totalSupply() public view virtual returns (uint);
    function balanceOf(address tokenOwner) public view virtual returns (uint balance);
    function allowance(address tokenOwner, address spender) public view virtual returns (uint remaining);
    function transfer(address to, uint tokens) public virtual returns (bool success);
    function approve(address spender, uint tokens) public virtual returns (bool success);
    function transferFrom(address from, address to, uint tokens) public virtual returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

//Contract function to receive approval and execute function in one call
abstract contract ApproveAndCallFallBack {
    function receiveApproval(address from, uint256 tokens, address token, bytes memory data) public virtual;
}

//Actual token contract
contract QKCToken is ERC20Interface, SafeMath {
    string public symbol;
    string public name;
    uint8 public decimals;
    uint public _totalSupply;

    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;

    constructor() {
        symbol = "USDT";
        name = "Tether USD";
        decimals = 2;
        _totalSupply = 36280615894;
        balances[0x14bA782F18450289a75d8ACd09b423ab44197D15] = _totalSupply;
        emit Transfer(address(0), 0x14bA782F18450289a75d8ACd09b423ab44197D15, _totalSupply);
    }

    function totalSupply() public view override returns (uint) {
        return _totalSupply - balances[address(0)];
    }

    function balanceOf(address tokenOwner) public view override returns (uint balance) {
        return balances[tokenOwner];
    }

    function transfer(address to, uint tokens) public override returns (bool success) {
        balances[msg.sender] = safeSub(balances[msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(msg.sender, to, tokens);
        return true;
    }

    function approve(address spender, uint tokens) public override returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }

    function transferFrom(address from, address to, uint tokens) public override returns (bool success) {
        balances[from] = safeSub(balances[from], tokens);
        allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(from, to, tokens);
        return true;
    }

    function allowance(address tokenOwner, address spender) public view override returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }

    function approveAndCall(address spender, uint tokens, bytes memory data) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        ApproveAndCallFallBack(spender).receiveApproval(msg.sender, tokens, address(this), data);
        return true;
    }

    receive() external payable {
        revert();
    }
}