/**
 * Code by Patrick Sava
 * "Spiru Haret" National College of Bucharest
 **/

# include "fstream"
# include "cstring"
# include "vector"
# include "queue"
# include "bitset"
# include "algorithm"
# include "map"
# include "set"
# include "unordered_map"
# include "deque"
# include "string"
# include "iomanip"
# include "cmath"
# include "stack"
# include "cassert"

const char IN [ ] =  "numarare.in" ;
const char OUT [ ] = "numarare.out" ;

using namespace std ;

# define pb push_back
# define mp make_pair
# define FORN( a , b , c ) for ( register int a = b ; a <= c ; ++ a )
# define FORNBACK( a , b , c ) for ( register int a = b ; a >= c ; -- a )

ifstream cin ( IN ) ;
ofstream cout ( OUT ) ;

const int MAX = 1e5 + 14 ;

int v [ MAX ] ;
int pali [ MAX ] ;

int main()
{
    int n ;
    cin >> n ;
    FORN ( i , 1 , n ) {
        cin >> v [ i ] ;
    }
    int center = 0 ;
    int R = 0 ;
    long long S = 0 ;
    FORN ( i , 2 , n - 1 )
    {
        int sim = 2 * center - i ;
        if ( i + 1 + pali [ sim ] < center + R ) {
            pali [ i ] = pali [ sim ] ;
        }
        else {
            pali [ i ] = R - i - 1 ;
            while ( pali [ i ] + 1 + 1 + i <= n and i - pali [ i ] - 1 >= 1 and v [ pali [ i ] + 1 + 1 + i ] + v [ i - pali [ i ] - 1 ] == v [ i ] + v [ i + 1 ] )
                pali [ i ] ++ ;
        }
        if ( i + pali [ i ] + 1 > R + center ) {
            R = pali [ i ] + 1 ;
            center = i ;
        }
        S += pali [ i ] ;
        S ++ ;
    }
    cout << ++ S << '\n' ;
    return 0;
}