Program lr28;
var k,a,b,c,x,z: integer;
d:real;
begin
write('№ equation: ');
readln(k);
writeln('variables:');
readln(x,z,a,b,c);
case k of
1: begin d:=(x-z)/(x+z); writeln(d); end;
2: begin d:=-b/(2*a); writeln(d); end;
3: begin d:=(a*a*a)/abs(x-z); writeln(d); end;
4: begin d:=sqrt(abs(b*b-4*a*c)); writeln(d); end;
else writeln('error');
end;
end.