var v:array[1..1000002] of integer;
    f,g:text;
    i,j,k,n,nr:integer;
begin
assign(f,'operatii.in');reset(f);
assign(g,'operatii.out');rewrite(g);
readln(f,n);
for i:=1 to n do
    read(f,v[i]);
i:=1;nr:=0;
while i<=n do
     if v[i]=0 then inc(i)
        else begin
            j:=i;
            while (v[j+1]<>0) and (j<n) do
                  inc(j);
            for k:=i to j do dec(v[k]);
            inc(nr);
        end;
writeln(g,nr);
close(g);
end.