foo.c: In function 'main':
foo.c:7:27: error: redeclaration of 'n' with no linkage
    7 |         int a1,a2,b1,b2,m,n,i;
      |                           ^
foo.c:5:13: note: previous declaration of 'n' with type 'int'
    5 |         int n;
      |             ^

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