//0009
#include <bits/stdc++.h>
using namespace std;

int main(){
    int n;
    while(cin>>n){
        if(n == 1) {
            cout<<0<<endl;
        }
        else if(n == 2){
            cout<<1<<endl;
        }
        else{
            int num[1000000] = {};
            for(int tmp = 2;tmp != n;tmp++){
                if(num[tmp] == 0)
                for(int i = tmp * 2;i <= n;i += i){
                    num[i] = 1;
                }
            }
            int count = 0;
            for(int i = 2;i != n;i++){
                if(num[i] == 0){
                    count++;
                }
            }
            cout<<count<<endl;
        }
    }
}