#include <iostream>
using namespace std;
int cif[10];
int main()
{
int n,lg=0,x,i,ramas;
cin>>n;
///punem cifrele intr-un vector
while(n)
{
cif[++lg]=n%10;
n/=10;
}
x=cif[1];
ramas=0;
for(i=1;i<=lg;i++)
if(cif[i]!=x)
cif[++ramas]=cif[i];
lg=ramas;
x=0;
if(lg<1)
cout<<"-1"<<"\n";
else
{
for(i=lg;i>=1;i--)
x=x*10+cif[i];
cout<<x<<"\n";
}
return 0;
}