#include <bits/stdc++.h>

using namespace std;

int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);
    int N;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin >> N;
    int p{0};
	int i, j, a[N+1];
	for (a[1] = 0, i = 2; i <= N; i++)
		a[i] = 1;
	for (i = 2; i <= N / 2; i++)
		for (j = 2; j <= N / i; j++)
			a[i*j] = 0;
	for (i = 1; i <= N; i++)
		if (a[i]) p++;
	fout << p;
	return 0;
}