#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;
}