25、有一分数序列：2/1,3/2,5/3.8/5,13/8,'''求前20项之和

/*
有一分数序列：2/1,3/2,5/3.8/5,13/8,'''求前20项之和
 */

#include <stdio.h>
#include <stdlib.h>

double getSum(int n)
{
    double fenzi = 2;
    double fenmu = 1;
//    int fenzi = 2;
//    int fenmu = 1;
    double sum = 0;
    for(int cnt = 1;cnt <= n;cnt ++)
    {
 //       sum += fenzi * 1.0 / fenmu;
        sum += (double) fenzi / fenmu;
        fenzi += fenmu;
        fenmu = fenzi - fenmu;
//        fenmu = fenzi ;    错误写法！！！！！
//        fenzi += fenmu ;
    }
    return sum;
}

int main()
{
    int n;
    scanf("%d", &n);
    printf("%f\n", getSum(n));
    int a = 3;
    int b = 2;
    double c = 1;
    c += (double) a / b;
    printf("%f", c);

    return 0;
}