求大佬指点

#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<limits.h>
#include<cmath>
#define ll long long
#define ld long double
using namespace std;

const int nmax = 30001;
int primehash[nmax];
int prime[nmax];

void Euler_mesh(int n) //欧拉筛
{
	int i, j;
	int pp = 0;
	for (i = 2; i <= n; i++)
	{
		if (!primehash[i]) //是素数
		{
			prime[++pp] = i;
		}
		for (j = 1; i * prime[j] <= n; j++)
		{
			primehash[i * prime[j]] = 1;
			if (i % prime[j] == 0)
			{
				break;
			}
		}

	}
}

int main()
{
	int n;
	cin >> n;
	Euler_mesh(30000);
	cout << prime[n] << endl;
}