#include <stdio.h>
#define Nmax 2000003

int n, i, j, prime;
char p[Nmax];

int main() {
	
	FILE *f = fopen("ciur.in", "r");
	FILE *g = fopen("ciur.out", "w");
	
	fscanf(f, "%d", &n);
	
	for (i = 2; i <= n; i++)
		if (!p[i]) {
			prime++;
			for (j = 2*i; j <= n; j += i)
				p[j] = 1;
		}
	
	fprintf(g, "%d", prime);
	
	fclose(f);
	fclose(g);
	
	return 0;
}