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

begin
assign(input,'operatii.in');reset(input);
assign(output,'operatii.out');rewrite(output);
readln(n);
for i:=1 to n do
        read(v[i]);
i:=1;
v[n+1]:=0;
while i<=n do
        begin
        while v[i]=0 do
                inc(i);
        max:=0;
        while v[i]<>0 do
                begin
                if v[i]>max then
                        max:=v[i];
                inc(i);
                end;
        s:=s+max;
        end;
writeln(s);
close(input);close(output);
end.