#include <fstream>
#include <cmath>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
short int prim[2000001];
int main()
{
    int n,i,d,contor=0,j;
    f>>n;
    for(i=2;i<=sqrt(n);i++){
        if(prim[i]==0)
            for(j=2*i;j<=n;j=j+i)
                prim[j]=1;
    }
    for(i=2;i<=n;i++)
        if(prim[i]==0)
            contor++;
    g<<contor;
}