bool is_prime(short int x)
{
for(int i=2;i<x;i++)
if(x%i==0)
return false;
return true;
}
long double largest_prime(short int x)
{
short int c=1;
long double z,y;
y=x;
while(y<pow(2,128))
{
for(int i=9;i>=1;i--)
{
z=i*pow(10,c)+y;
if(is_prime(z))
{cout<<z<<endl;
c++;
y=z;}
}
}
return y;
}