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