#include <fstream>

using namespace std;
bool ciur[2000000];
int c;
int main()
{
    ifstream f("ciur.in");
    ofstream f2("ciur.out");
    int N;
    f >> N;
    for (int j=4; j<N; j+=2)
        ciur[j]=1;
    for (int i=3; i*i<N; i+=2)
        if (!ciur[i])
            for (int j=i*i; j<N; j+= 2*i)

                ciur[j] = 1;

    for (int i=2; i<N; ++i){
        if (!ciur[i])
            c++;
    }
    f2 << c;

}