#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

ifstream f("ciur.in");
ofstream of("ciur.out");

int main()
{
    int n, i, cnt = 0, j;
    f >> n;

    vector<int> v(n + 1, 1);

    for(i = 2; i <= n; i++)
        if( v[i] ) {
            cnt++;
            for(j = i + i; j <= n; j += i)
                v[j] = 0;
        }

    of << cnt;

    return 0;
}