#include <stdio.h>
#include <conio.h>

int ciur(int n)
{
	bool *a = new bool[n+1];
	for(int k = 0; k<=n; k++)
	{
		a[k] = false;
	}
	int noprime = 0;
	int i,j;
	for(i = 2; i<=n; i++)
	{
		if(a[i] == false)
		{
			noprime ++;
			for(j = i*2; j<=n; j+=i)
				a[j] = true;
		}
	}
	delete [] a;
	return noprime;
}

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

	int n;

	fscanf(f,"%d",&n);
	fprintf(g,"%d",ciur(n));
}