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escrow.sol

pragma solidity 0.4.24;

contract Escrow {
    
    address public buyer;
    address public seller;
    address public arbiter;
    
    constructor(address _seller, address _arbiter) public {
        buyer = msg.sender;
        seller = _seller;
        arbiter = _arbiter;
    }
    
    function paySeller() public {
        if(msg.sender == buyer || msg.sender == arbiter) {
            seller.transfer(address(this).balance);
        }
    }
    
    function refundBuyer() public {
        if(msg.sender == seller || msg.sender == arbiter) {
            buyer.transfer(address(this).balance);
        }
    }
    
    function fund() public payable returns (bool) {
        return true;
    }
    
    function getBalance() public constant returns (uint) {
        return address(this).balance;
    }
}

storage.sol

pragma solidity ^0.4.0;

contract Storage {
    uint storedData;

    function set(uint x) public {
        storedData = x;
    }

    function get() public view returns (uint) {
        return storedData;
    }
}