#include <bits/stdc++.h>
using namespace std;
char x,z;
long long int y,w; 
int main()
{
	cin>>x>>y>>z>>w;
	if(x==z)
	{
		if(x>='a' && x<='z')
		{
			if(z>='a' && z<='z')
			{
				cout<<"valid"<<"\n";
				if(w>=y)
				{
					cout<<w-y+1;
				}
				else
				{
					cout<<y-w+1;
				}
				return 0;
			}
		}
	}
	else cout<<"Invalid"<<endl<<-1<<endl;
	return 0;
}