hi. new here. Im a freshman at UCSB and im taking my first c++ class. I got this assignment in class and i was hoping for some tips.

The value of pi to 15 decimal places is PI = 3.141592653589793 . . . Your job is to write a
program that can be used to find decent approximations to PI. More specifically, your program must find
integers N and D such that the fraction N/D is the best possible approximation to PI and such that D <
1,000,000.

I have already set up nested while loops to chug through the fractions and limited the numerator to n <= 3145926. I also set a if condition right in between the while to reduce the numer of times it goest through the calculations by narrowing the numbers between 3 and 4( like pi). such that if( 3*d < n && 4*d > n){

Now the thing works but it takes about 6 hrs to run and for this project the instructor wants us to make one that runs in 2 min or less. I was wondering if anyone has any tips that may help.
thank you
bw