#include <cstdio>

int n, count;
bool non[2000000];

int main() {
	FILE * in = fopen("ciur.in", "rt");
	FILE * out = fopen("ciur.out", "wt");

	fscanf(in, "%d", &n);
	for (int i = 2; i < n; ++i) {
		if (!non[i]) {
			++count;
			for (int j = i; j < n; j += i) {
				non[j] = 1;
			}
		}
	}
	fprintf(out, "%d\n", count);

	fclose(in);
	fclose(out);
}