program pirma_uzd;
    const n = 100;
    var duom, rez : text;
        grandinesDaliu, i : integer;
        bendraVarza : real;
        varzos : array[1..n] of real;
 
procedure Skaitom;
    var j, laidininku, laidinkoVarza : integer;
        varza : real;
begin
    assign(duom, 'Duom1.txt');
    reset(duom);
 
    ReadLn(duom, grandinesDaliu);
    Writeln(grandinesDaliu);
 
    for i := 1 to grandinesDaliu do
        begin
            varza := 0;
            Read(duom, laidininku);
            for j := 1 to laidininku do
                begin
                    Read(duom, laidinkoVarza);
                    varza := varza + (1/laidinkoVarza);
                end;
            Varzos[i] := varza;
            Readln(duom);
        end;
    close(duom);
end;
 
begin
    Skaitom;
    for i := 1 to grandinesDaliu do
            bendraVarza := bendraVarza + (1 / Varzos[i]);
 
    assign(rez, 'Rez1.txt');
    rewrite(rez);
    Write(rez, bendraVarza:0:2);
    close(rez);
end.