#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
ifstream in("operatii.in");
ofstream out("operatii.out");
const int maxn = 7000005;
char T[maxn];
long long s;
int n;
void rezolva()
{
    in.getline(T, maxn);
    in.getline(T, maxn);
    int sz = strlen(T);
    int nr = 0;
    int last = 0;
    for(int i = 0; i < sz; i++)
    {
        if(T[i] >= '0' && T[i] <= '9')
            nr = nr * 10 + T[i] - '0';
        else
        {
            if(nr - last > 0)
                s = s + nr - last;
            last = nr;
            nr = 0;
        }
    }
    if(nr - last > 0)
        s = s + nr - last;
}
int main()
{
    in >> n;
    rezolva();
    out << s << "\n";
    return 0;
}