#include <iostream>
#include <stdlib.h>
#include <fstream>
using namespace std;

int main() {
    int n, i, j, contor = 0;
    ifstream in;
    in.open("ciur.in");
    in >> n;
    char *prim = (char*)calloc(n,sizeof(char));
    for (i = 3; i <= n; i += 2) {
        if (prim[i] == 0) {
            contor++;
            for (j = 2 * i; j <= n; j += i)
                prim[j] = 1;
        }
    }
    ofstream out;
    out.open("ciur.out");
    out << contor + 1;
    out.close();
    in.close();
    return 0;
}