function buyPoints (uint256 _itemId) payable public {
    require(msg.value > 0);
    require(ownerOf(_itemId) == msg.sender);
    require(!isContract(msg.sender));
    
    uint256 point = msg.value.mul(L).div(1000000000000000000);
    
    pointOfItem[_itemId] = point;
    timeOfItem[_itemId] = Time_call();
    
    owner.transfer(msg.value);
    
    pointArrayOfArray[_itemId].push(point);
    timeArrayOfArray[_itemId].push(Time_call());
  }