#include <cstdio>
#include <cstring>
#include <iostream>
#include <math.h>

int main() {
	
	FILE *fin = fopen("ciur.in", "r");
	FILE *fout = fopen("ciur.out", "w");
	
	int n, count;
	
	fscanf(fin, "%d", &n);
	fclose(fin);
	
	bool ciur[n + 1];
	memset(ciur, true, sizeof(bool) * (n + 1));
	
	count = -2;
	for (int i = 2; i < sqrt(n); i++) {
		
		for (int j = i * i; j < n; j += i) {
			ciur[j] = false;
		}
	}
	
	for (int i = 1; i <= n; i++) {
		if (ciur[i]) {
			count++;
		}
	}
	
	fprintf(fout, "%d", count);
	fclose(fout);
	
	return 0;
}