using namespace std;



#define fisier "ciur"

#ifdef fisier
    #include <fstream>
    ifstream in(fisier ".in");
    ofstream out(fisier ".out");
#else
    #include <iostream>
    #define in cin
    #define out cout
#endif



bool v[2000001];
int n;



void build() {

    int i, j, np2 = n/2, npi;

    for (i = 2; i <= np2; i++) {

        for (j = i+i; j <= n; j+=i) {

            v[j] = 1;

        }

    }

}



int main() {

    in >> n;

    build();

    int s = 0;
    for (int i = 2; i <= n; i++) {

        if (!v[i]) s++;

    }

    out << s;


}