#include<iostream>
#include<cmath>
#include<vector>
using namespace std;

int main(){
    int n;
    while(cin >> n){
        int numOfPrime = 0;
        bool isPrime[n-1];
        for(int i=2;i<=n;++i){
            isPrime[i-2] = true;
        }
        for(int i=2;i<=sqrt(n);++i){
            if(!isPrime[i-2]){
                continue;
            }
            for(int j=i;j<=n;++j){
                if(j%i == 0 && i != j){
                    isPrime[j-2] = false;
                }
            }
        }
        for(int i=2;i<n;++i){
            if(isPrime[i-2]){
                ++numOfPrime;
            }
        }
        cout << numOfPrime << endl;
    }
}