#include <stdio.h>   
  
int N, cnt;   
char prim[2000005];   
  
int main(void)   
{   
    int i, j;   
       
    freopen("ciur.in", "r", stdin);   
    freopen("ciur.out", "w", stdout);   
  
    scanf("%d", &N);   
    for (i = 2; i <= N; ++i)   
        prim[i] = 1;   
    for (i = 2; i <= N; ++i)
        if (prim[i])   
        {   
            ++cnt;   
            for (j = i+i; j <= N; j += i)   
                prim[j] = 0;   
        }   
  
    printf("%d\n", cnt);   
  
    return 0;   
}