#include<fstream>
using namespace std;
int main()
{ifstream f("ciur.in");
ofstream g("ciur.out");
int i,j,n,k=1;
f>>n;
int a[n+1],b[n+1];
for(i=3;i<=n;i++)
	a[i]=0;
for(i=3;i<=n;i=i+2)
if(a[i]==0)
{
for(j=i*i;j<=n;j=j+i)
	a[j]=1;
k++;
}
g<<k;
}