#include <stdio.h>
typedef enum { false, true } bool;

int main () {
	int n, k, i, j;
	bool c[2000001];

	FILE *inp, *outp;
	inp = fopen("ciur.in", "r");
	fscanf(inp,"%d", &n);
	fclose(inp);

	for (i = 2; i <= n; i ++) {
		c[i] = 1;
	}
	for( i = 2; i <= n; i ++) {
		if (c[i] == 1) {
			k ++;
			for (j = i + i; j <= n; j += i) {
				c[j] = 0;
			}
		}
	}

	outp = fopen("ciur.out", "w");
	fprintf(outp, "%d", k);
	fclose(outp);

	return 0;
}