#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;
													}