求最大公约数
............\.classpath
............\.project
............\.settings
............\.........\org.eclipse.jdt.core.prefs
............\bin
............\...\Gcd.class
............\...\Gcd1.class
............\...\ged2.class
............\src
............\...\Gcd.java
............\...\Gcd1.java
............\...\ged2.java