foo.cc: In function 'int main()':
foo.cc:9:13: error: 'n' was not declared in this scope
    9 |  for(i=2;i<=n-1;i++)
      |             ^
foo.cc:19:5: warning: this 'else' clause does not guard... [-Wmisleading-indentation]
   19 |     else
      |     ^~~~
foo.cc:21:2: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'else'
   21 |  return 0;
      |  ^~~~~~
foo.cc:7:13: warning: unused variable 's' [-Wunused-variable]
    7 |     int m,i,s=0;
      |             ^

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