#include <fstream>
#include <cmath>
using namespace std;
int v[700000];
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n,i,j,x,nr=0;
    fin>>n;
    x=sqrt(n);
    for(i=4;i<=n;i=i+2)
        v[i]=1;
    for(i=3;i<=x;i=i+2)
    {
        if(v[i]==0)
            for(j=i*i;j<=n;j=j+2*i)
            {
                v[j]=1;
            }
    }
    for(i=2;i<=n;i++)
        if(v[i]==0)
            nr++;
    fout<<nr;
    return 0;
}