#include<cstdio>
#include<bitset>
#define maxn 2000001
using namespace std;

bitset<maxn> prim;
int i , j , n , cnt;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%d\n",&n);
	
	for ( i = 3 ; i * i <= n ; i += 2 )
		if (prim[i] == 0 ) {
			++cnt;
			for( j = i * i ; j <= n ; j +=i )
				prim[j] = 1;
		}
	for( ; i <= n ; i += 2 )
		if ( prim[i] == 0  ) cnt++;

printf("%d\n",cnt + 1);

return 0;
}