1 #include <algorithm> 2 #include <iostream> 3 #include <iomanip> 4 #include <cstring> 5 #include <climits> 6 #include <complex> 7 #include <fstream> 8 #include <cassert> 9 #include <cstdio>10 #include <bitset>11 #include <vector>12 #include <deque>13 #include <queue>14 #include <stack>15 #include <ctime>16 #include <set>17 #include <map>18 #include <cmath>19 using namespace std;20 #define fr first21 #define sc second22 #define cl clear23 #define BUG puts("here!!!")24 #define W(a) while(a--)25 #define pb(a) push_back(a)26 #define Rint(a) scanf("%d", &a)27 #define Rll(a) scanf("%I64d", &a)28 #define Rs(a) scanf("%s", a)29 #define Cin(a) cin >> a30 #define FRead() freopen("in", "r", stdin)31 #define FWrite() freopen("out", "w", stdout)32 #define Rep(i, len) for(int i = 0; i < (len); i++)33 #define For(i, a, len) for(int i = (a); i < (len); i++)34 #define Cls(a) memset((a), 0, sizeof(a))35 #define Clr(a, x) memset((a), (x), sizeof(a))36 #define Full(a) memset((a), 0x7f7f7f, sizeof(a))37 #define lrt rt << 138 #define rrt rt << 1 | 139 #define pi 3.1415926535940 #define RT return41 #define lowbit(x) x & (-x)42 #define onecnt(x) __builtin_popcount(x)43 typedef long long LL;44 typedef long double LD;45 typedef unsigned long long ULL;46 typedef pair<int, int> pii;47 typedef pair<string, int> psi;48 typedef pair<LL, LL> pll;49 typedef map<string, int> msi;50 typedef vector<int> vi;51 typedef vector<LL> vl;52 typedef vector<vl> vvl;53 typedef vector<bool> vb;54 55 const int maxn = 1000010;56 char tn[2*maxn];57 double ret[maxn];58 LL n;59 60 signed main() {61     Cls(ret);62     double tmp = .0;63     For(i, 1, 1000000) {64         tmp += double(1.0)/double((LL)i*i);65         ret[i] = tmp;66     }67     while(~Rs(tn)) {68         int len = strlen(tn);69         if(len >= 7) n = 999999;70         else sscanf(tn, "%I64d", &n);71         printf("%.5lf\n", ret[n]);72     }73     RT 0;74 }