#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");



int main()
{int n,i,j,r=0;
char a[2000000];
f>>n;
for(i=2;i<=n;i++)
if(a[i]!=2){r++;
for(j=2*i;j<=n;j+=i)
a[j]=2;
}
g << r;
return 0;
}