#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int c[2000001],v[2000000];
int i,j,k,n;

int main()
{
    f >> n;

    for ( i = 2; i <= n ; i++ )
        for ( j = 2 ; j * i <= n; j++ )
            c[i*j] = 1;
    for(int i=2; i<=n; i++)
        if(c[i]==0)
            v[++k]=i;


    i=0;
    while(v[i+1]<=n and i+1<=k)
        i++;
    g<<i;
    return 0;
}