#include <iostream>
#include <fstream>
#include <cmath>
#include <bitset>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bitset <2000001>v;
int main()
{
    int n,cnt=0,i,j;
    f>>n;
    v[0]=v[1]=1;
    for (i=2;i<=sqrt(n);i++)
        if (v[i]==0)
            for (j=i*2;j<=n;j+=i) v[j]=1;

    for (i=1;i<=n;i++)
        if (v[i]!=1) cnt++;
    g<<cnt;
    return 0;
}