#include <iostream>
#include "stdio.h"
#include "string.h"
#include "math.h"
 
using namespace std;
 
bool isPrime[100000000];
int main() {
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n, k = 0;
    scanf("%d", &n);
    memset(isPrime, true,sizeof(bool) * n);
    for(int i = 2; i <= n;i++){
        if(isPrime[i]){
            k++;
            for(int j = i + i; j <= n;j += i)
                isPrime[j] = 0;
        }
    }
    printf("%d", k);
    return 0;
}