#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
int N, cnt=0;
char prim[2000005];
    int i, j;
    in>>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;
        }

    out<< cnt;

    return 0;
}