由不等式可推导得，a1+a2+a3的最小值在处取得

#include<algorithm>
#include<iostream>
#include<iomanip>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
using namespace std;
const int INF=0x3f3f3f3f;
int read()
{
   int s=0,bj=0;
   char ch=getchar();
   while(ch<'0'||ch>'9')bj|=(ch=='-'),ch=getchar();
   while(ch>='0'&&ch<='9')s=(s<<1)+(s<<3)+(ch^48),ch=getchar();
   return bj?-s:s;
}
void printnum(int x)
{
    if(x>9)printnum(x/10);
    putchar(x%10^48);
}
void print(int x,char ch)
{
    if(x<0){putchar('-');x=-x;}
    printnum(x);putchar(ch);
}
int n;
int main()
{
    n=read();
    printf("%.3lf",(double)pow(n,1.0/3)*3);
    return 0;
}