#include <stdio.h>

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

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

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

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

	return 0;
}