#define _CRT_SECURE_NO_DEPRECATE

#include <stdio.h>

int n, nrp;	bool P[2000001];

int main(){
	int i, j;

	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	scanf("%d", &n); nrp = n - 1;
	for (i = 2; i <= n; i++){
		if (!P[i]){
			for (j = 2 * i; j <= n; j += i){
				nrp -= 1 - P[j];
				P[j] = 1;
			}
		}
	}
	printf("%d", nrp);

	return 0;
}