#include <fstream>
using namespace std;
const int NMax = 2000002;
char Ciur[NMax];
int main()
{
    int n,i,j,nr=1;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for(i=3;i*i<=n;i++)
    {
        for(j = i * i;j <= n; j = j + 2*i)
            Ciur[j]=1;
    }
    if(n==1) g<<"0";
    else
    {
        for(i=3;i<=n;i=i+2)
            if(!Ciur[i])nr++;
        g<<nr;
    }
}