#include <fstream>
const std::string programName = "ciur";
std::ifstream f(programName + ".in");
std::ofstream g(programName + ".out");
const int MAX= 2e6;
int main() {
    char prim[MAX + 5];
    int N;
    f >> N;
    for (int i = 3; i <= N; ++i)
        prim[i] = 1;
    int counter = 0;
    for (int i = 3; i <= N; ++i)
        if (prim[i]) {
            ++counter;
            for (int j = i + i; j <= N; j += i)
                prim[j] = 0;
        }
    g << counter;
    return 0x0;
}