#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
	freopen("s")
    int n, num = 0;
    bool ciur[2000001] = {0};
    
    fin >> n;
 
    for (int i = 0; i <= n; i += 2)
    	ciur[i] = true;
    ciur[1] = true;
    ciur[2] = false;
    for (int i = 3; i <= n; i += 2)
    	if(ciur[i] == 0)
    		for (int j = 2 * i; j <= n; j += i)
    			ciur[j] = true;

    for (int i = 2; i <= n; ++i)
    	if (ciur[i] == 0)
    		num++;
    fout << num;

	return 0;
}