#include<fstream>
#include<bitset>
#define dim 2000001
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, nr, i, j;
bitset <dim> v;
int main() {
    fin >> n;
    for (i = 2; i <= n; i++) {
        if (v[i] == 0) {
            nr++;
            for (j = i + i; j <= n; j = j + i)
                v[j] = 1;
        }
    }
    fout << nr;
}