1604A-Era.cpp

#include <cstdio>

int main(){

    long t; scanf("%ld", &t);
    while(t--){
        long n; scanf("%ld", &n);
        long res(0);
        for(long p = 1; p <= n; p++){
            long x; scanf("%ld", &x);
            long diff = x - p;
            res = (res > diff) ? res : diff;
        }

        printf("%ld\n", res);
    }

}