#include <fstream>

using namespace std;

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

#define lmax 2000005
long unsigned int k,h,v2[lmax]; bool v[lmax];

int main()
{
    for(unsigned long int i=2;i<=lmax;i++)
    {
        if(v[i]==0) {v[i]=1; v2[h++]=i;
        for(unsigned long int j=i+i;j<=lmax;j+=i) v[j]=1;}
    }

    fin>>k;
    for(h=0;v2[h]<=k;h++);
    fout<<h;
}