#include<fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
long n,i=2,j,nr;
bool v[2000005];
int main()
{
    cin>>n;
    while(i<=n)
    {
        if(v[i]==0)
        for(j=i+i;j<=n;j=j+i)v[j]=1;
        i++;
    }
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            nr++;
        }
    }
    cout<<nr;
}