# include<cstdio>
using namespace std;
# define MAXSIZE 1000000
char p[MAXSIZE];
int prim(int n)
{int nr=1,i,j;
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;i*2+1<=n;i++)
	if(p[i]==0)	
		nr++;
return nr;
}
int main()
{FILE *f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");
int n;
fscanf(f,"%d",&n);
fprintf(g,"%d",prim(n));
}