#include<iostream>
#include<cstring>
using namespace std;
const int N = 100010;
long long w[N], f[2][N];
int main()
{
    int n;
    cin >> n;
    for(int i = 1; i <= n; i++) cin >> w[i];
    memset(f, -0x3f, sizeof(f));
    for(int i = 0; i <= n; i++) f[0][i] = 0;

    f[1][1] = f[0][0] - w[1];
    for(int i = 1; i <= n; i++)
    {
        f[0][i] = max(f[0][i - 1], f[1][i - 1] + w[i]);
        if(i != 1)
        f[1][i] = max(f[0][i - 2] - w[i], f[1][i - 1]); 
    }

//  for(int i = 1; i <= n; i++) cout << f[0][i] << " " << f[1][i] << endl;

    cout << f[0][n] << endl;

    return 0;   
}