#include<fstream>
#include<vector>
using namespace std;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    unsigned int n,i,s;
    fin>>n;
    s=0;
    vector<bool> x = {};
    for(i=0;i<n;i++)
        x.push_back(1);
    x.at(0)=x.at(1)=0;
    for(i=2;i<n;++i)
        if(x.at(i)==1)
        {
            for(int j=2*i;j<n;j+=i)
                x.at(j)=0;
            ++s;
        }
        fout<<s;
}