Decompose the natural numbers A and B into prime factors: A=a*5, B=b*5*7, if the least common multiple of A and B is 210, then what is the greatest common divisor.
把自然数A和B分解质因数得：A=a*5，B=b*5*7，如果A和B的最小公倍数是210，那么最大公约数是多少．
<result>5</result>