#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;
}