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, s;



void build() {

    int i, j, npi;

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

                v[j] = 1;

            }

        }

    }

}



int main() {

    in >> n;

    build();

    out << s;


}