#include<stdio.h>   
#include<string.h>   
#define N 2000009   
  
long n;   
char v[N];   
long prime[1009];   
int m;   
long k;   
int main(){   
    freopen("ciur.in", "r", stdin);      
    freopen("ciur.out", "w", stdout);   
       
    scanf("%ld" ,&n);   
    long i,j;   
    for(i=2; i<=n; ++i)   
        if (v[i]==0)   
            for (++k, j=2; j*i<=n; ++j)   
                v[j*i]=1;   
    printf("%ld\n", k);   
    
           
       
       
       
    return 0;   
}