#include <stdio.h>
#include <stdlib.h>
#define MAXINT 2000001

_Bool v[MAXINT];
int i, n,j,ans;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d", &n);
    for (i = 3; i <= n; i += 2)
        if(v[i] == 0){
            ans++;
            for (j = i + i ; j <= n; j += i)
                v[j] = 1;
        }

    if(n >= 2)  ans++;

    printf("%d\n",ans);
    return 0;
}