foo.cc: In function 'int main()':
foo.cc:30:8: warning: unused variable 'gcd' [-Wunused-variable]
     ll gcd=exgcd(a,b,x,y);
        ^~~
foo.cc:28:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%lld%lld",&a,&b);
     ~~~~~^~~~~~~~~~~~~~~~~~

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