#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;
   }