#include<cstdio>
using namespace std;
int n,k=1;//p[100]
bool u[2000002];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int i,j;
    scanf("%d",&n);
    //p[k++]=2;
    for(i=3;i<=n;i+=2)
    {
        if(!u[i])
        {
            k++;//p[k++]=i;
            for(j=i*i;j<=n;j+=2*i)
                u[j]=true;
        }
    }
    printf("%d\n",k);
    //for(i=0;i<k;i++)
    //    printf("%d ",p[i]);
    return 0;
}