foo.c: In function 'GCD':
foo.c:4:15: warning: left-hand operand of comma expression has no effect [-Wunused-value]
  else return(y,x%y);
               ^
foo.c: In function 'main':
foo.c:9:11: warning: unknown conversion type character 'l' in format [-Wformat=]
  scanf("%lld%lld",&x,&y);
           ^
foo.c:9:15: warning: unknown conversion type character 'l' in format [-Wformat=]
  scanf("%lld%lld",&x,&y);
               ^
foo.c:9:8: warning: too many arguments for format [-Wformat-extra-args]
  scanf("%lld%lld",&x,&y);
        ^~~~~~~~~~
foo.c:9:11: warning: unknown conversion type character 'l' in format [-Wformat=]
  scanf("%lld%lld",&x,&y);
           ^
foo.c:9:15: warning: unknown conversion type character 'l' in format [-Wformat=]
  scanf("%lld%lld",&x,&y);
               ^
foo.c:9:8: warning: too many arguments for format [-Wformat-extra-args]
  scanf("%lld%lld",&x,&y);
        ^~~~~~~~~~
foo.c:13:11: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long int' [-Wformat=]
  printf("%d",count*2);
           ^
foo.c:13:11: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long int' [-Wformat=]