#include<stdio.h>
int main()
{
	FILE *f, *g;
	f=fopen ("ciur.in","r");
	g=fopen ("ciur.out","w");
	char v[2000000];
	int i,n,j,nr=0;
	fscanf(f,"%d",&n);
	for(i=2;i<=n;i++)
		v[i]='1';
	for(i=2;i<=n; )
	{
		for(j=i*i;j<=n;j=j+i)
			v[j]='0';
		do
			i++;
			while(v[i]=='0' && i<=n);
	}
	for(i=2;i<=n;i++)
		if(v[i]=='1')
			nr++;
	fprintf(g,"%d",nr);
	fclose(f);
	fclose(g);
	return 0;
}