#include<iostream>
#include<cmath>
#define REP(i,n) for(int i=0;i<n;i++)
using namespace std;

bool isPrime[1000000];

void setIsPrime(int x) {
    isPrime[1] = true;
	for(int i = 1; i < x; i++) {
		int n = (int)sqrt(i);
		int yakusu = 0;
		for(int j = 1; j<=n; j++) {
			if(i%j==0) yakusu++;
			if(yakusu > 2) break;
		}
		if (yakusu==1) {
			isPrime[i] = true;
		}
	}
}

int numPrimes(int x) {
    int cnt = 0;
    for (int n=1; n <= x; n++) {
        if (isPrime[n]) cnt++;
    }
    return cnt - 1;
}

int main(){
    int x;
    setIsPrime(1000000);
	while(cin >> x) {
		cout << numPrimes(x) << endl;
	}
    return 0;
}