# include <cstdio>
using namespace std;
# define N 100000
char p[N];
int main()
{int i,j,n,nr=1;
FILE *f=fopen("ciur.in","r"),*g=fopen("ciur.out","w"	);
fscanf(f,"%d",&n);
for(i=1;((i*i)<<1)+(i<<1)<=n;i++)
	{if(p[i]==0){
		for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
			{p[j]=1;}
	}}
for(i=1;2*i+1<=n;i++)
	if(p[i]==0)nr++;
fprintf(g,"%d",nr);
}