#include <stdio.h>
#include <iostream>

using namespace std;

int prim[2000005];

int N, cnt;

int main(void)
{
    int i, j;

    freopen("ciur.in", "r", stdin);
   freopen("ciur.out", "w", stdout);

    scanf("%d", &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;
        }

   printf("%d\n", cnt);

    return 0;
}