#include <stdio.h>
 
char sieve[2000001];
 
int main () {
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    long long n, i, j; scanf("%lld", &n);
    long long k = 0;
    for(i = 2; i <= n; i++) sieve[i] = 1;
    for(i = 2; i <= n; i++)
        if(sieve[i] == 1) {
            k++;
            for(j = i * i; j <= n; j+=i)
                sieve[j] = 0;
        }
    printf("%lld", k);
    return 0;
}