#include <stdio.h>   
  
int N, nr;
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])
	{
	    ++nr;
	    for (j = i+i; j <= N; j += i)
		prim[j] = 0;
	}

    printf("%d\n",nr);   
  
    return 0;   
}