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

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

int n, i, j, k = 1;
bool v[2000000];
int main() {
    fin >> n;
    for(i = 3; i <= n; i += 2)
        v[i] = 1;
    for(i = 3; i <= n; i += 2) {
        if(v[i]) {
            k++;
            for(j = i + i; j <= n; j += i)
                v[j] = 0;
        }
    }
    fout << k;
    fin.close();
    fout.close();
    return 0;
}