New guy and programming problem

[Skirmitch]

Hey guys, I'm new here. I'm an electronics engineer and I mainly work in the computer science field specifically in data analysis and mainly machinne learning. I'm a programmer in many languages (for data analysis I use Python) and I'm a fan of vintage things when things were made to last forever. I've been out hunting for a calculator for some time now since I really don't like my dad's Casio fx something (1980's long calculator with full pc style keyboard programmable in basic). When I was studying I used the HP48g+ but I lost it (stolen) and now I want something a bit smaller. I'm a believer that RPN is the only practical method for a calculator (if u r going to input large things that need reviewing u r better with a computer) and so I started looking around. After a long search, I sadly found out that I liked the HP42s over everything and so here I am sitting waiting for SwissMicros to release their tribute while I use Free42 on my phone. I watched all of Logan's videos (yes, from every calculator, not only the 42S) and just now I wrote my first program and it is to get the total resistance of 2 parallel resistors (and want to write one for 3 and 4 parallel ones and some transistor's formulas for my hobbies) and I found myself in my first problem: If I have the variables R1 and R2 already set with the right values and I call the function, it runs perfectly but if I have everything cleared and I input the variables when the function asks for them, the program doesn't run. If after that first run I call it again, it works perfectly (since the variables are already stored). Can anyone help me?

LBL "PAR2"
INPUT "R1"
1/X
INPUT "R2"
1/X
+
1/X
END


For those who don't know the formula, it is 1 / ( 1/R1 + 1/R2)

thanks in advance and also thanks for running such an awesome web