function freeze(uint256 _value, uint256 _duration) public {
        require(_value > 0 && _value <= balances[msg.sender]);
        require(_duration > 60);

        balances[msg.sender] = balances[msg.sender].sub(_value);

        
        uint256 timestamp = block.timestamp;
        freezed[msg.sender] = Schedule({
            amount: _value,
            start: timestamp,
            cliff: timestamp,
            duration: _duration,
            released: 0,
            lastReleased: timestamp
        });

        emit Freeze(msg.sender, _value, 0, _duration);
    }