foo.c: In function 'main':
foo.c:9:5: warning: implicit declaration of function 'ys' [-Wimplicit-function-declaration]
    9 |  yu=ys(fm,fz);
      |     ^~
foo.c:5:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    5 |  scanf("%d%d",&b1,&a1);
      |  ^~~~~~~~~~~~~~~~~~~~~
foo.c:6:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    6 |  scanf("%d%d",&b2,&a2);
      |  ^~~~~~~~~~~~~~~~~~~~~

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