#include<fstream.h>

int n,i,j,k=0;
char s[2000001];
int main()
{ifstream f("ciur.in");ofstream g("ciur.out");f>>n;
for(i=2;i<=n;i++) 
	s[i]=1;
for(i=2;i<=n;i++)
{if(s[i]==1)
{k++;
for(j=i+i;j<=n;j+=i) s[j]=0;}}g<<k;

return 0;}