View Code of Problem 71

#include<bits/stdc++.h>
using namespace std;
#define max 100000
//2 3 5 8 13  21
//1 2 3 5  8  13
int main(){
	double sum = 0;
	int n,shang = 2, xia = 1,k = 0;
	cin>>n;
	while(n--){
		sum = sum + shang *1.0/ xia ;
		k = xia;
		xia  = shang;
		shang = shang + k;		
	}
	printf("%.2lf",sum);
	return 0;
}