function vestedAmount (address account) private view returns (uint256) {
        if (block.timestamp < beneficiary[account].cliff) {
            return 0;
        } else if (block.timestamp >= beneficiary[account].start.add(beneficiary[account].duration)) {
            return beneficiary[account].totalAmount;
        } else {
            return beneficiary[account].totalAmount.mul(
                block.timestamp.sub(beneficiary[account].start)
            ).div(beneficiary[account].duration);
        }
    }