# include <stdio.h>

# define input "ciur.in"
# define output "ciur.out"

# define max 2000001

int n,i,j,res;
bool a[max];

int main()
{
    freopen(input, "r", stdin);
    freopen(output, "w", stdout);
    
    scanf("%d",&n);
    
    for(i=2;i<=n;i++)
       if(!a[i])
       {
           res++;
           for(j=i+i;j<=n;j+=i)
               a[j] = 1; 
       }
    
    printf("%d",res);
    
    return 0;
}