import std.conv, std.functional, std.range, std.stdio, std.string; import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons; import core.bitop; class EOFException : Throwable { this() { super("EOF"); } } string[] tokens; string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; } int readInt() { return readToken.to!int; } long readLong() { return readToken.to!long; } real readReal() { return readToken.to!real; } bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } } bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } } int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; } int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); } int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); } /* (x2, y2): min y (< 0) (x1, y1): max y (x <= x2) oper [y1, y2) y1' >= 2 y1 - y2 > 2 y1 ==> 1 + log_2(N) steps */ enum INF = 10^^9; enum K = 20; void main() { try { for (; ; ) { const N = readInt; auto S = readToken; auto dp = new int[2 * K + 1]; dp[] = -INF; dp[0] = 0; foreach (i; 0 .. N + 1) { foreach (k; 0 .. 2 * K + 1) { if (dp[k] < 0) { dp[k] = -INF; } } foreach (k; 0 .. 2 * K) { chmax(dp[k + 1], dp[k]); } if (i < N) { final switch (S[i]) { case '+': { foreach (k; 0 .. 2 * K + 1) { dp[k] += (-1)^^(k & 1); } } break; case '-': { foreach (k; 0 .. 2 * K + 1) { dp[k] -= (-1)^^(k & 1); } } break; case '?': { dp[] += 1; } break; } } } int ans = K + 1; foreach (k; 0 .. K + 1) { if (dp[2 * k] >= 0) { ans = k; break; } } writeln(ans); } } catch (EOFException e) { } }