// http://en.wikipedia.org/wiki/Euclidean_algorithm
// https://medium.com/i-math/why-does-the-euclidean-algorithm-work-aaf43bd3288e

// gcd.tc - 8/25/11, 9/7/18

gcd int a,b [
 if (b==0) return a
 else return gcd b,a%b
 ]

main [
 int a,b
 printf "%center a (e.g. 1071) : ",10
 a=gn
 printf "%center b (e.g. 462) : ",10
 b=gn
 printf "%cthe greatest common divisor of %d and %d is %d%c",10,a,b,gcd(a,b),10
 ]