can someone explain what is happening here?

Question

i tried to make a program that does the figonashi number, and it worked. The interesting is that the program decrease his speed of execution when it has a to high limit(the maximum size of the answer): whit 8 it doesn't work, 7 too slow ,6 slow, 5 normal speed. I elevated(or raised) the limit so i'm talking about the number of nines. (It doesn't work in the sofware of sololearn, it only say "don't output" after 5 nines of elevated).
https://code.sololearn.com/cnY25bUYXcH2/?ref=app