#include<iostream>
#include<fstream>
using namespace std;
int N, cnt;
char prim[2000005];
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main(void)
{
    int i, j;
    fin >> N;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i + i; j <= N; j += i)
                prim[j] = 0;
        }

    fout<<cnt;
    return 0;
}