#include <iostream>
#include <fstream>
#define LL long long
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,j,i,nr=0;
bool ap[2000001];
int main()
{
    f >> n;
    for(i=2;i<=n;i++)
        if(ap[i]==false)
        {
            nr++;
            for(j=i+i;j<=n;j+=i)
                ap[j]=1;
        }
    g<<nr<<'\n';
    return 0;
}