#include <iostream>
using namespace std;
int main()
{
    int prime[80000];
    int ptr=2;
    prime[0] = 2;
    prime[1] = 3;
    for(int num=5; num<1000000; num+=2){
        bool f = false;
        for(int i = 0; i<ptr; i++){
            if (prime[i]*prime[i] > num) break;
            if (num%prime[i]==0) {
                f = true;
                break;
            }
        }
        if(!f) prime[ptr++] = num;
    }
    prime[ptr]=1000001;
    int n;
    while(cin >> n){
        int k=0;
        for(;prime[k]<=n;k++);
        cout << k << endl;
    }
     
    return 0;
}
