#include <bits/stdc++.h>
#define nmax 2000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, sol, i, j;
char c[nmax];
int main()
{
    fin >> n;
    for(i = 2; i <= n; ++i)
        c[i] = 0;
    for(i = 2; i <= n; ++i)
        if(c[i] == 0)
        {
            sol++;
            for(j = i + i; j <= n; j += i)
                c[j] = 1;
        }
    fout << sol;
    return 0;
}