hdu5879 Cure

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<iostream>
 4 #include<cstring>
 5 #include<queue>
 6 #include<cmath>
 7 using namespace std;
 8 const int N = 1000010;
 9 const double pi = acos(-1.0);
10 char a[N];
11 double sum[N];
12 
13 int main(){
14     int i, l, x;
15     for(int i = 1; i < N; ++i)
16         sum[i] = sum[i - 1] + 1.0/i/i;
17     while(~scanf("%s",a)){
18         l = strlen(a);
19         if(l >= 7)printf("%.5lf\n",pi*pi/6);
20         else{
21             for(x = i = 0; i < l; ++i)
22                 x = 10 * x + a[i] - ‘0‘;
23             printf("%.5lf\n", sum[x]);
24         }
25     }
26     return 0;
27 }