// editor4
#include<iostream>
using namespace std;
int main()
{
    int slide1,slide2,slide3;
    cin>>slide1>>slide2>>slide>>3;
    bool is valid=(slide1+slide2+slide3)&&
    (slide1+slide3>slide2)&&(slide2+slide3>slide1);
    cout<<(is valid?"valid":"invalid");
    return 0;
}