contract P {
  mapping(address => uint) public balanceOf;
  uint public totalSupply;

  modifier check {
    _;
    assert(this.balance >= totalSupply);
  }

  function dee(uint amount) payable check {
    balanceOf[msg.sender] += amount;
    totalSupply += amount;
  }

  function ex(address to, uint value) payable check {
    if (balanceOf[msg.sender] >= value) {
      balanceOf[to] += value;
      balanceOf[msg.sender] -= value;
    }
  }

  function eff() payable check {
    uint balance = balanceOf[msg.sender];
    if (msg.sender.call.value(balance)()) {
      totalSupply -= balance;
      balanceOf[msg.sender] = 0;
    }
  }
}