#include <stdio.h>
#include <stdlib.h>
 
int main(){
    int n, result = 0;
    char *a;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d",&n);
    a =  (char *)calloc(n,  sizeof(char));
    for(int i = 2; i <= n;i++)
    {
        if(a[i] == 0){
            for(int j = i+i; j <= n; j+=i)
                a[j] = 1;            
            result ++;
        }
    }
    printf("%d",result);
	return 0;
}