#include<stdio.h>
int main()
{
	FILE *in, *out;

	int n, i, j, c, t=0;

	in = fopen("d://Cpp//infoarena//ciur.in", "rt");
	out = fopen("d://Cpp//infoarena//ciur.out", "wt");

	fscanf(in, "%d", &n);

	for(i=2;i<=n;i++)
	{
		c=0;
		for(j=2;j<i;j++)
			if(i%j==0)
				c++;

		if(c==0)
			t++;
	}

	fprintf(out, "%d", t);

	fcloseall();

	return 0;
}