#include<fstream.h>
#define MAX 2000002
long n;
int nr=0,a[MAX];
ifstream f("ciur.in");
ofstream g("ciur.out");


int main()
{long i,j;
f>>n;
for(i=2;i<=n;i++)
{if(!a[i]){nr++;
	    for(j=2*i;j<=n;j+=i)
	    a[j]=1;
	   }
}
g<<nr;
g.close();
f.close();
return 0;
}