#include <iostream>
#include <fstream>
using namespace std;
char a[2000010];
int main()
{
    int n,i,j,k=0;
    ifstream f ("ciur.in");
    ofstream g ("ciur.out");
    f>>n;
    for (i = 2; i <= n;++i)
        a[i] = 1;
    for (i = 2;i <= n;++i)
        if (a[i])
        {
            k++;
            for (j = i*2;j <= n;j += i)
                a[j] = 0;
        }
    g<<k;
    return 0;
}