#include<bits/stdc++.h>
using namespace std;
int main(){
	char x,z;
	int w,y,a;
	cin>>x>>z>>y>>w;
	if(x==z){
		if(y>=1 && w<=100){
			cout<<"valid"<<endl;
			if(y<=w){
				cout<<"-1";
			}else{
				a=w-y+1;
				cout<<a;	
			}		
		}else{
			cout<<"Invalid"<<endl;		
		}
	}else{
		cout<<"Invalid"<<endl;	
	}	
	return 0;
}