#include <fstream>
#include <iostream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

#define MAX 2000000

bool a[MAX+9];

int main()
{
    int n,i,j,k;
    a[0]=a[1]=1;
    fin>>n;
    k=0;
    for(i=2;i<MAX;i++)
        if(!a[i]&&n){
            for(j=i*i;j<=MAX;j+=i)
                a[j]=1;
            k++;n--;
        }
    fout<<k;
    return 0;
}