var
fmax,fmin,o:real;
n:integer;


begin

write('vvedite fmax:');
readln(fmax);
write('vvedite fmin:');
readln(fmin);
write('vvedite n:');
readln(n);

o:=((fmax-fmin)/exp(n*ln(2)))/2;
writeln('o=',o:6:3);

readln;
end.