/**
 *    author:  tđq
**/
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const ll nmax = 1e6 + 1;

ll n, d = 0;
bool check (ll x)
{
   for (ll i = 2; i <= sqrt(x); ++i)
   if (x % i == 0) return false;
   return x > 1;
}

int main()
{

 //freopen(task".inp" , "r" , stdin);
 //freopen(task".out" , "w" , stdout);

 ios::sync_with_stdio(false);
 cin.tie(0);

 cin >> n;
 ll i;
 while (d <= n)
 {
    i++;
    if (check(i))
    {
       d++;
       if (d == n)
       {
          return cout << i, 0;
       }
    }
 }
 return 0;
}

`@` Cách 1:

#include <iostream>
using namespace std;
int main()
{
int n;
cin>>n;
int a[1225]={0};
for (int i=2,d= 0; i<=1224;++i) {
if (a[i]==0) {
++d;
if (d==n) {
cout<<i<<endl;
break;
}
for (int j=i*2;j<=1224;j+=i) {
a[j]=1;
}
}
}
return 0;
}

`@` Cách 2

#include <iostream>
#include <vector>
using namespace std;
const int l=200;
int main() {
int n;
cin>>n;
vector<int>ok;
for (int n2=2;ok.size()<l;++n2) {
bool ktra=true;
for (int ok:ok) {
if (ok*ok>n2) break;
if (n2%ok==0) {
ktra=false;
break;
}
}
if (ktra) ok.push_back(n2);
}
cout<<ok[n-1]<<"\n";
return 0;
}