import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv,
    std.functional, std.math, std.numeric, std.range, std.stdio, std.string,
    std.random, std.typecons, std.container;

ulong MAX = 1_000_100, MOD = 1_000_000_007, INF = 1_000_000_000_000;
alias sread = () => readln.chomp();
alias lread(T = long) = () => readln.chomp.to!(T);
alias aryread(T = long) = () => readln.split.to!(T[]);
alias Pair = Tuple!(string, "x", long, "y");
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);

void main()
{
    auto n = lread();
    auto h = aryread();
    long cnt, left;
    while (h.sum > 0)
    {
        long iter = n, m = h[left];
        foreach (i; iota(left, n))
        {
            if(h[i] == 0)
            {
                iter = i;
                break;
            }
            m = min(h[i], m);
        }
        foreach (i; iota(iter - left))
        {
            // writeln(left + i);
            h[i + left] -= m;
        }
        left = h.left_idx();
        // h.writeln();
        cnt += m;
    }
    cnt.writeln();
}

auto left_idx(T)(T ary)
{
    long iter;
    while (iter < ary.length && ary[iter] == 0)
        iter++;
    return iter;
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}
