#include <iostream>
#include <cstdio>
using namespace std;
int main() {
int t, n, a[100002], min, max, gap;
scanf("%d", &t);
while(t--) {
max=0; min=1000000; gap=0;
scanf("%d", &n);
for(int i=0; i<n; i++) {
scanf("%d", &a[i]);
}
for(int i=0; i<n-1; i++) for(int j=i+1; j<n; j++) if(a[j]-a[i]>gap) gap=a[j]-a[i];
if(gap) printf("%d\n", gap);
else printf("UNFIT\n");
}
return 0;
}
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