#include <cstdio>
#include <cstring>
#define MAX 2000009
using namespace std;
int cnt,n;
char v[MAX];
int euler(int x)
{
    int i,j;
    memset(v,'1',MAX);
    for(i=2;i<=n;++i)
        if(v[i])
        {
            cnt++;
            for(j=i+i;j<=n;j+=i)v[j]=0;
        }
    return cnt;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    printf("%d\n",euler(n));
    return 0;
}