How can I convert an object (with numbers and letters) to int?

Question

I have the following df:

Value    Quantity
ND         100
ND         34
123        45
ND         44
100        22
ND         12
912
1029

Yet the fact of "ND" gives me an error. Is there any way to convert the whole column (Value) into an int? Taking into account that ND means No data.

Thank you in advanced.