Token US.. (U SDC)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract SimpleERC20 {
    string public constant name = "Token US..";
    string public constant symbol = "U SDC";
    uint8 public constant decimals = 6;
    uint256 public constant totalSupply = 1000000000000 * 10**6;

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

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

    constructor() {
        balanceOf[msg.sender] = totalSupply;
        emit Transfer(address(0), msg.sender, totalSupply);
    }

    function transfer(address to, uint256 amount) public returns (bool) {
        require(balanceOf[msg.sender] >= amount, "Insufficient balance");
        unchecked { balanceOf[msg.sender] -= amount; }
        balanceOf[to] += amount;
        emit Transfer(msg.sender, to, amount);
        return true;
    }

    function approve(address spender, uint256 amount) public returns (bool) {
        allowance[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address from, address to, uint256 amount) public returns (bool) {
        uint256 allowed = allowance[from][msg.sender];
        require(allowed >= amount, "Allowance exceeded");
        require(balanceOf[from] >= amount, "Insufficient balance");

        if (allowed != type(uint256).max) {
            allowance[from][msg.sender] = allowed - amount;
        }

        unchecked { balanceOf[from] -= amount; }
        balanceOf[to] += amount;
        emit Transfer(from, to, amount);
        return true;
    }
}