【题目链接】
http://www.lydsy.com/JudgeOnline/problem.php?id=1053
【题解】
反素数有一个性质：质数的次幂递减。然后暴力就行了。
/* --------------
user Vanisher
problem bzoj-1053
----------------*/
# include <bits/stdc++.h>
# define ll long long
# define inf 0x3f3f3f3f
# define N 110
using namespace std;
ll read(){
ll tmp=0, fh=1; char ch=getchar();
while (ch<'0'||ch>'9'){if (ch=='-') fh=-1; ch=getchar();}
while (ch>='0'&&ch<='9'){tmp=tmp*10+ch-'0'; ch=getchar();}
return tmp*fh;
}
ll p[N],mx,n,now,j,pnum,mxnum;
void dfs(ll k, ll les, ll x, ll num){
if (num>mxnum||num==mxnum&&x<mx)
mx=x, mxnum=num;
ll i=p[k], j=1;
while (x*i<=n&&j<=les){
dfs(k+1,j,x*i,num*(j+1));
j++; i=i*p[k];
}
}
int main(){
n=read(); now=1, j=1;
while (now<=n){
j++; bool f=true;
for (ll i=2; i*i<=j; i++)
if (j%i==0){
f=false;
break;
}
if (f){
now=now*j;
p[++pnum]=j;
}
}
dfs(1,inf,1,1);
printf("%lld
",mx);
return 0;
}