#include <stdio.h>

int N, cnt;
char prim[2000005];

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;