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