#include<cstdio>
#include<cmath>
using namespace std;
char v[2000010];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,i,d,prime=0,a,j;
    scanf("%d",&n);
    for(i=2;i<=n;++i)
    {
        if(v[i]==0)
        {
            for(j=i+i;j<=n;j+=i)
                v[j]=1;
            prime++;
        }



    }
    printf("%d",prime);
}