//Beiland Arnold - ciur 07.11.2012
#include <fstream>
#include <vector>
#include <cmath>

int main(){
    std::ifstream fin("ciur.in");
    std::ofstream fout("ciur.out");
    unsigned int n,sqrtn;
    fin>>n;
    sqrtn=std::sqrt(n);
    std::vector<bool> ciur(n/2,false);
    unsigned int nr=1; //2 is prime
    for(unsigned int i=3;i<=n;i+=2)
        if(!ciur[i/2-1]){
            ++nr;
            if(i<=sqrtn)
                for(unsigned int j=i*i;j<=n;j+=2*i) ciur[j/2-1]=true;
        }
    fout<<nr<<'\n';
}