var n,i,max,st,dr,min:longint;
    v:array[1..1000010] of longint;
    s:int64;

begin
assign(input,'operatii.in');reset(input);
assign(output,'operatii.out');rewrite(output);
readln(n);
for i:=1 to n do
        read(v[i]);
for i:=1 to n do
        if (v[i]>v[i+1]) then
                s:=s+v[i]-v[i+1];
writeln(s);
close(input);close(output);
end.