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contracts...22_CoinTimer.sol

pragma solidity >=0.7.0 <0.9.0;

contract Coin {
    address public minter;
    uint contractCreatedAt;
    mapping(address => uint) public balances;

    event Sent(address from, address to, uint amount);
 
    constructor() {
        minter = msg.sender;
        contractCreatedAt = block.timestamp;
    }

    modifier onlyMinter {
      require(msg.sender == minter);
      _;
    }

    modifier checkAmount(uint _amount) {
       require(_amount < 1e60);
       _;
    }

    modifier checkbalance(uint _amount) {
      require(_amount <= balances[msg.sender], "Insufficient Balance!");
      _;
    }

    modifier checkReleaseTime {
        require (block.timestamp >= contractCreatedAt + 20, "Too soon");
        _;
    }

    function mint(address _receiver, uint _amount) public onlyMinter checkAmount(_amount) {
        balances[_receiver] += _amount;
    }
    
    function send(address _receiver, uint _amount) public checkReleaseTime checkbalance(_amount) {
        balances[msg.sender] -= _amount;
        balances[_receiver] += _amount;
        emit Sent(msg.sender, _receiver, _amount);

    }
}