foo.cc: In function 'int main()':
foo.cc:7:35: error: 'a1g' was not declared in this scope
     cout << (a2 - a1) * (n - 1) + a1g << endl;
                                   ^~~
foo.cc:7:35: note: suggested alternative: 'a1'
     cout << (a2 - a1) * (n - 1) + a1g << endl;
                                   ^~~
                                   a1

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