var
    n, m        : longint;
    i, i1       : longint;
    matr        : array [1..500, 1..500] of longint;
    sto, str    : array [1..500] of longint;
    min     : longint;

    pch     : array [0..100100] of boolean;

    fin     : text;

begin
    assign (fin, 'in.txt'); reset(fin);
    readln (fin, n, m);
    {writeln(n, m);}
    for i:=1 to n do begin
        for i1:=1 to m do begin
            read(fin, matr[i, i1]);

        end;
        readln(fin);
    end;



    { Простые числа }

    for i:=1 to 100100 do begin
        pch[i]:=true;
    end;
    pch[0]:=false;
    pch[1]:=false;

    for i:=1 to 100100 do begin
        if pch[i] then begin
            i1:=i*2;
            while i1<=100100 do begin
                pch[i1]:=false;
                i1:=i1+i;
            end;
        end;
    end;


    { Считаем "расстояние" }

    for i:=1 to n do begin
        str[i] := 0;
    end;

    for i:=1 to m do begin
        sto[i] := 0;
    end;

    for i:=1 to n do begin
        for i1:=1 to m do begin
            while not pch[matr[i, i1]] do begin
                inc (matr[i, i1]);
                inc (str[i]);
                inc (sto[i1]);
            end;
        end;
    end;

    { В поисках минимума }

    min := str[1];

    for i:=1 to n do
        if str[i]<min then min:=str[i];

    for i:=1 to m do
        if sto[i]<min then min:=sto[i];

    writeln(min);
    {writeln(matr[1, 1]);}
    close (fin);
end.