#include<bits/stdc++.h>
using namespace std;
long y,w; char x,z;
int main(){
    scanf("%c%ld%c%ld",&x,&y,&z,&w);
    if((x<'a'||y<'a')||(x!=y))
      printf("Invalid\n-1");
    else
      printf("valid\n%ld",(y<=w?w-y+1:y-w+1));
    return 0;
}