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