#include <fstream>
#include <vector>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

unsigned int n;
vector<bool> ciur;

int main(){
    fin>>n;
    ciur = vector<bool>(n+1,true);
    unsigned int counter=0;
    for(int i=2;i<=n;i++)
        if(ciur[i]) {
            counter++;
            for (int j = (i << 1); j <= n; j += i)
                ciur[i] = false;
        }
    fout<<counter;
    return 0;
}