#include <iostream>
#include <fstream>
using namespace std;
ifstream in("operatii.in");
ofstream out("operatii.out");
string str;
long long s;
int n;
void rezolva()
{
    getline(in, str);
    getline(in, str);
    int sz = str.size();
    int nr = 0;
    int last = 0;
    for(int i = 0; i < sz; i++)
    {
        if(str[i] >= '0' && str[i] <= '9')
            nr = nr * 10 + str[i] - '0';
        else
        {
            if(nr - last > 0)
                s = s + nr - last;
            last = nr;
            nr = 0;
        }
    }
    s = s + nr - last;
}
int main()
{
    in >> n;
    rezolva();
    out << s << "\n";
    return 0;
}