#include<fstream.h>   
ifstream f("ciur.in");   
ofstream g("ciur.out");   
int n,i,j,b[10000],k;   
char a[2000005];   
int main()   
{   
f>>n;   
for(i=2;i<=n;i++)   
    {if(!a[i])   
        {for(j=i*2;j<=n;j+=i)   
              a[j]=1;   
       ++k;}   
    }   
g<<k<<'\n';   
return 0;   
}