#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int i,j,nr,n,y;
bool a[2000001];
int main()
{f>>n;
nr=1;
y=(int)(double)sqrt((double)n);
for(i=3;i<=y;i=i+2)
	if(a[i]==0)
		for(j=i*i;j<=n;j=j+i)
			a[j]=1;
	
for(i=3;i<=n;i=i+2)
	if(a[i]==0)
		++nr;
g<<nr<<'\n';
f.close();
g.close();
return 0;
}