1629 B君的圆锥

 #include <iostream>
 #include <queue>
 #include <stack>
 #include <cstdio>
 #include <vector>
 #include <map>
 #include <set>
 #include <bitset>
 #include <algorithm>
 #include <cmath>
 #include <cstring>
 #include <cstdlib>
 #include <string>
 #include <sstream>
 #include <time.h>
 #define x first
 #define y second
 #define pb push_back
 #define mp make_pair
 #define lson l,m,rt*2
 #define rson m+1,r,rt*2+1
 #define mt(A,B) memset(A,B,sizeof(A))
 #define mod 1000000007
 using namespace std;
 typedef long long LL;
 const double PI = acos(-);
 const int N=2e5+;
 const int inf = 0x3f3f3f3f;
 const LL INF=0x3f3f3f3f3f3f3f3fLL;
 //已知圆锥的表面积S求最大的体积：V=S*sqrt(S/(72*PI))
 int main()
 {
 #ifdef Local
     freopen("data.txt","r",stdin);
 #endif
     double n;
     cin>>n;
     printf("%lf\n",n*sqrt(n/(*PI)));
 #ifdef Local
     cerr << "time: " << (LL) clock() *  / CLOCKS_PER_SEC << " ms" << endl;
 #endif
 }