#include <fstream>
#include <cmath>

using namespace std;

int n, ok, i, j, ri, prime;

char v[2000010];


int main(){
	
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	
	fin>>n;
	for (i=2;i<=n;i++) {
		if (v[i] == 0) {
			prime ++;
			for (j=i+i;j<=n; j+=i)
				v[j] = 1;
		}
	}
	fout<<prime<<"\n";
	return 0;
}