#include <fstream>
#define MAX 2000002
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
char v[MAX];
int n;
int ciur()
{
    int nr=1,i;

    for(i=3;i*i<=n;i=i+2)
        if(v[i]==0)
        {
            nr++;
            for(int j=i*i;j<=n;j=j+i+i)
                v[j]=1;
        }
    for(;i<=n;i=i+2)
        if(v[i]==0)
            nr++;
    return nr;
}
int main()
{
    f>>n;
    g<<ciur();
}