#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
const int LG_MAX=100000;

int a[LG_MAX+1],v[LG_MAX],j,i,nr,n;

int main()
{
    f>>n;
    nr=1;
    v[1]=2;
    for(i=4;i<=n;i+=2)
        a[i]=1;
    for(i=3;i<=n;i+=2)
    {
        if(a[i]==0)
        {
            nr++;
            v[nr]=i;
            for(j=i*2;j<=n;j+=i)
                a[j]=1;
        }
    }
    g<<nr;
    return 0;
}