A possible readf int bug

[Matilda]

I'm trying to read from stdin and then print an integer value. 
This is how my code looks like:
```d
import std.stdio;
import std.conv;
import std.string;

void main()
{
     writeln("Input your variant (1 - 10):");
     int key;
     //readf(" %d", &key);
     //readf!" %d"(key);

     key = readln.strip.to!int;

     writefln("Your variant is: %d", key);
}
```
The problem is that the programme doesn't work if I try to use 
one of the commented readf functions. It doesn't print the last 
phrase. There is no error message. It just waits for nothing 
apparently. It works with the stip.to!int line, so the problem 
must be with readf.
I'm kind of new to this language and I don't have much experience 
with programming in general, so I have no way to know if it's 
just me being dumb or I've accidently found a bug.

I use DMD32 D Compiler v2.097.0-dirty