#include <stdio.h>
int main() {
	FILE *in = fopen("ciur.in", "r");
	FILE *out = fopen("ciur.out", "w");
	int n;
	fscanf(in, "%d", &n);
	n++;
	unsigned char arr[n];
	arr[0] = 0;
	arr[1] = 0;
	for(int i = 2; i < n; i++) {
		arr[i] = 1;
	}
	for(int i = 2; i*i < n; i++) {
		for (int j = i * i; j < n; j += i) {
			arr[j] = 0;
		}
	}
	int c = 0;
	for(int i = 0; i < n; i++) {
		if(arr[i]) {
			c++;
		}
	}
	fprintf(out, "%d", c);
}