34 lines
575 B
C++
34 lines
575 B
C++
#include<cstdio>
|
|
#include<cstring>
|
|
#include<algorithm>
|
|
#include<cmath>
|
|
using namespace std;
|
|
|
|
const int N = 1e6 + 5;
|
|
|
|
char a[N];
|
|
double sum[N];
|
|
|
|
void yu()
|
|
{
|
|
for(int i = 1 ; i < N ; i++){
|
|
sum[i] = sum[i - 1] + (double)1/i/i;
|
|
}
|
|
}
|
|
int main()
|
|
{
|
|
yu();
|
|
while(~scanf("%s",a)){
|
|
int l = strlen(a);
|
|
if(l >= 7) printf("%.5lf\n",sum[1000000]);
|
|
else{
|
|
int n = 0;
|
|
for(int i = 0 ; i < l ; i++){
|
|
n = n * 10 + a[i] - '0';
|
|
}
|
|
printf("%.5lf\n",sum[n]);
|
|
}
|
|
}
|
|
return 0;
|
|
}
|