#include <fstream>
#include <vector>
using namespace std;
ifstream cin("operatii.in");
ofstream cout("operatii.out");
vector<long long> v;
int main()
{
    long long n,a,rasp=0;
    cin>>n;
    cin>>a,v.push_back(a);
    for(long long i=1;i<n;++i)
    {
        cin>>a;
        if(a!=v[v.size()-1]) v.push_back(a);
    }
    if(v[0]>v[1])
        rasp+=1LL*v[0];
    for(long long i=1;i<v.size()-1;++i)
    {
        if(v[i]<v[i-1] and v[i]<v[i+1])
            rasp-=1LL*v[i];
        else if(v[i]>v[i-1] and v[i]>v[i+1])
            rasp+=1LL*v[i];
    }
    if(v[v.size()-1]>v[v.size()-2])
        rasp+=1LL*v[v.size()-1];
    cout<<rasp;
    return 0;
}