#!/usr/bin/python
# -*- coding: UTF-8 -*-

'''
题目：有一分数序列：2/1，3/2，5/3，8/5，13/8，21/13...求出这个数列的前20项之和。
'''

a = 2.0;
b = 1.0;
s = 0.0;
for n in range(1,21):
    s += a / b;
    b,a = a , a + b;
print s;

s = 0.0;
for n in range(1,21):
    s += a / b;
    b,a = a , a + b;
print s;

# result
'''
32.6602607986
32.360679776
'''
