#include <iostream>
#include <cstring>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
unsigned char v[250000];

int main()
{
    memset(v,0,sizeof(v));
    int n,i,j,s=0;
    f>>n;
    for(i=2;i<=n;i++)
        if((v[i>>3]>>i%8)&1!=0)
        {
            s++;
            for(j=i<<1;j<=n;j+=i)
                v[j>>3]|=(1<<j%8);
        }
    g<<s;
    return 0;
}