//SESC USU SUDO RM -RF

var a,b,c,d,i:integer;
begin
read(a,b);
d:=0;
for i:=1 to b do
begin
read(c);
if d<0 then d:=0;
d:=d-(a-c);
end;
if d > 0 then writeln (d) else writeln ('0');
end.

Edited by author 01.12.2012 17:40

Sudo -rm -rf Rulez By Me!