#include<cstdio>

FILE *f = fopen("ciur.in", "r");
FILE *g = fopen("ciur.out", "w");

bool a[2000001];

int main() {
	int n;
	fscanf(f, "%d", &n);
	int s = 0;
	for(int i = 2; i<=n; i++) {
		if(a[i]) continue;
		int x = i*2;
		s++;
		while(x <= n) {
			a[x] = true;
			x+=i;
		}
	}
	fprintf(g,"%d", s);
}