A - Era

https://codeforces.com/contest/1604/submission/133618725

CodeForces/1604/A/A.cpp

@@ -0,0 +1,19 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int t, n, a, ans;
+
+int main() {
+    cin >> t;
+    while (t--) {
+        ans = 0;
+        cin >> n;
+        for (int i = 1; i <= n; i++) {
+            cin >> a;
+            ans = max(ans, a - i);
+        }
+        cout << ans << endl;
+    }
+    return 0;
+}