#include <iostream>
#include <fstream>
#define Max 10000
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,i,j,ok[Max],nr;
int main()
{fin>>n;
for(i=2;i<n;i++)
    ok[i]=0;//presupunem ca toate numerele pana la n sunt prime
for(i=2;i*i<n;i++)
    for(j=2;i*j<n;j++)
    ok[i*j]=1;
for(i=2;i<n;i++)
    if(ok[i]==0) nr++;
    fout << nr;
    return 0;
}