#include <iostream>
#include <bitset>
#include <fstream>
using namespace std;
bitset <10000000> ciur;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int d,n,i,S=0;
    fin>>n;
    for (d=2;d*d<=n;d++)
        if (ciur[d]==0)
          for ( i = d + d; i <= n; i = i + d) ciur[i]=1;
    for (i=2;i<=n;i++) if (ciur[i]==0) S++;
    fout<<S;
    return 0;
}