#include<iostream>
using namespace std;
int N;
string S;
int dp[60];
main()
{
	cin>>N>>S;
	for(char c:S)
	{
		for(int i=0;i<60;i++)dp[i]+=c=='?'?1:c=='+'?i%2==0?1:-1:i%2==1?1:-1;
		for(int i=1;i<60;i++)dp[i]=max(dp[i],dp[i-1]);
		for(int i=0;i<60;i++)if(dp[i]<0)dp[i]=-1e9;
	}
	int k=0;
	while(dp[k]<0)k++;
	cout<<(k+1)/2<<endl;
}