https://www.luogu.com.cn/record/196924125

#include<bits/stdc++.h>
using namespace std;
double s;
int n;
long long t=1;
int main()
{
	cin>>n;
	for(int i=1;i<=n;i++)
	t*=i,s+=1/(t*1.0);
	printf("%.10lf",s+1);
    return 0;
}

https://www.luogu.com.cn/record/196924143

#include<bits/stdc++.h>
using namespace std;
long double s;
int n;
long long t=1;
int main()
{
	cin>>n;
	for(int i=1;i<=n;i++)
	t*=i,s+=1/(t*1.0);
	printf("%.10lf",s+1);
    return 0;
}

rt