#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
const int MA=2000000;
bool v[MA+5];
int main()
{
    int n,s=1,i,j;
    cin>>n;
    for(i=4;i<=n;i=i+2)
        v[i]=1;
    for(i=3;i<=n;i++)
        if(v[i]==0)
        {
        s++;
        for(j=2*i;j<=n;j=j+i)
            v[j]=1;
        }
    cout<<s;
    cin.close();
    cout.close();
    return 0;
}