/in/foo.cc: In function 'int main()':
/in/foo.cc:9:23: warning: 'n' is used uninitialized [-Wuninitialized]
    9 |         for (int i=3;i<=n;i++)
      |                      ~^~~
/in/foo.cc:6:23: note: 'n' was declared here
    6 |         int a,b,s1,s2,n;
      |                       ^