#include<fstream>

using namespace std;
int n,ciur[200000],i,j;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{ int k= 0;
    fin>>n;
    for(i=2;i<=n;++i)
    if(ciur[i]==1)
    for(j=1;j<=n;j=j+i)
    ciur[j]=0;
    for(i=2;i<=n;i++)
    if(ciur[i]==1)
    k++;
    fout<<k;
    fin.close();
    fout.close();
    system ("pause");}