% 2017 Round 1B, Problem A, in Picat, by Afa Zhou
% https://code.google.com/codejam/contest/8294486/dashboard#s=p0
% Steed 2: Cruise Control

import util.

main =>
    T = read_line().to_int(),
    foreach (TC in 1..T)
        [D,N] = [to_int(Token) : Token in read_line().split()],
        KS = [(to_int(KToken),to_int(SToken)) : _ in 1..N, [KToken,SToken] = read_line().split()].sort(),
        once dc(KS,D,Time),
        printf("Case #%w: %.6f\n", TC, D/Time)
    end.

dc([(K,S)],D,T) =>
    T = (D-K)/S.
dc([(K1,S1),(K2,S2)|KS],D,T),
    S1 > S2
=>
    K = (K1*S2-K2*S1)/(S2-S1),
    T1 = (K-K1)/S1,    
    (K < D ->
        K22 = K-T1*S2,
        dc([(K22,S2)|KS],D,T)
    ;
        dc([(K1,S1)|KS],D,T)
    ).
dc([P,_|KS],D,T) =>
    dc([P|KS],D,T).
  
     
     
    
  
  

picat-lang.org