//最大公约数(greatest common divisor)，运用递归

int gcd(int a,int b){//注意a要求大于b

    return !b?a:gcd(b,a%b);

}

//最小公倍数(Lowest Common Multiple,LCM)的求值运用到最大公约数

int lcm(int a,int b){

    int d=gcd(a,b);

    return a/d*b;

}