#include <fstream>

using namespace std;

ifstream f("operatii.in");
ofstream g("operatii.out");

int n,i,x,ot,oc,v[1000001];
void calc (int i) {
  if (v[i]==0) {
    ot+=oc;oc=0;
    return;
  }
  if (v[i]>v[i-1]) {
    oc=oc+v[i]-v[i-1];
    return;
  }
  return;
}

int main () {
  f >> n;
  for (i=1;i<=n+1;i++) {
    f >> v[i];
    calc(i);
  }
  g << ot << '\n';
  f.close();g.close();
  return 0;
}