#include <fstream>
#include <cmath>
using namespace std;
#define MAX 100000001
char v[MAX];
int n, nr;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
    int i, j, lim;
    fin>>n;
    nr = 1;
    lim = sqrt(n);
    for(i=3; i<=lim; i=i+2)
        if(!v[i]){
            for(j=i*i; j<=n; j=j+i+i)
                v[j] = 1;
            nr++;
        }
    for( ;i<=n; i=i+2)
        if(!v[i]) nr++;
    fout<<nr;
    return 0;
}