View Code of Problem 71

#include<bits/stdc++.h>
using namespace std;
int main() {
	int N,a[100000],b[100000];
	double sum;
	cin>>N;
	a[0]=1;
	b[0]=2;
	sum=2;
	for(int i=1; i<N; i++) {
		b[i]=a[i-1]+b[i-1];
		a[i]=b[i-1];
		sum+=b[i]*1.0/a[i];
	}
	printf("%.2f", sum);
}