#include <fstream>
#include <iostream>
#include <cmath>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int v[100000];
int n,i,j,cont;
int main()
{
    fin >>n;
    for (i=2;i<=n;i++)
        v[i]=1;
    for (i=2;i<=sqrt(n);i++)
            for (j=2;j<=n/i;j++)
                v[i*j]=0;
    for (i=2;i<=n;i++)
        if (v[i]==1)
            cont=cont+1;
    fout <<cont;
    return 0;
}