#include <fstream.h>
#include<cmath>
using namespace std;
int main()
{long int N, d, c, OK, i;
ifstream f("ciur.in");
ofstream h("ciur.out");
f>>N;

if (N<3)
	c=1;
else
	if (N<5)
		c=2;
	else
		if (N<7)
			c=3;
		else
			if (N>=7)
				
{c=3;
d=7;
while (d<=N)
{OK=1;
i=3;
do
{if (d%i==0)
	OK=0;
i=i+2;
}
while ((i<=int(sqrt((double)d)))&&(OK==1));
if (OK==1)
	c=c+1;
d=d+2;
}
}
h<<c<<endl;
f.close();
h.close();
return 0;
}