Failing all the test cases:
#include<bits/stdc++.h>
using namespace std;
#define ll long long
void prime_sieve(int p,int n)
{
for(ll i=3;i<=1000000;i+=2)
{
p[i]=1;
}
for(ll i=3;i<=1000000;i+=2)
{
if(p[i]==1)
{
for(ll j=ii;j<=1000000;j+=i)
{
p[j]=0;
}
}
}
p[2]=1;
int nth=0,k=2;
while(nth<=n)
{
if(p[k]==1)
{
nth++;
}
k++;
}
cout<<nth<<endl;
return;
}
int main()
{
int n;
cin>>n;
int p[1000000]={0};
prime_sieve(p,n);
return 0;
}