#include<stdio.h>

#define input "ciur.in"
#define output "ciur.out"

#define dim 500000

long long unsigned n, a[dim], cont;

int main()
{
	FILE *in, *out;

	in = fopen (input, "r");
	out = fopen (output, "w");

	long long unsigned i, j;

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

	for(i=2; i<=n; i++)

		for(j=i+i; j<=n; j+=i)

			a[j] = 1;

	for(i=2; i<=n; i++)

		if(!a[i])

			cont++;

	fprintf(out, "%lld", cont);

	return 0;

}