#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    unsigned int *n,num_primes=0;
    scanf("%u",&n);

    bool *sieve=(bool *)calloc(n,sizeof(bool));

    for(unsigned int i=2;i<=n;i++)
        if(sieve[i]==false)
    {
        num_primes+=1;

        for(unsigned int j=i*i;j<=n;j+=i)
            sieve[j]=true;

    }

    printf("%u",num_primes);
    free(sieve);

    return 0;
}