// QuangBuiCP
#ifndef LOCAL
#pragma GCC optimize(3)
#pragma GCC target("avx2")
#endif // LOCAL
#include "bits/stdc++.h"
using namespace std;
#define SZ(a) (int)(a).size()
#define ALL(a) (a).begin(),(a).end()
const int N = 5005;
int n;
int a[N];
int pref[N];
int dp[N][N];
int f[N];
int Brute() {
int ret = 0;
for (int mask = 0; mask < (1 << n); ++mask) {
int cnt = 0;
set<int> prv, cur;
int pos = 0, layer = 0;
bool no = false;
for (int i = 1; i < n; ++i) {
int x1 = 0, x2 = 0;
if (mask >> i & 1) {
x1 = 1;
}
if (mask >> (i - 1) & 1) {
x2 = 1;
}
if (x1 && x2) {
no = true;
break;
}
}
if (no) {
continue;
}
for (int i = 0; i < n; ++i) {
if (mask >> i & 1) {
layer++;
prv = cur;
cur.clear();
}
int sign = 1;
if (layer % 2) {
sign *= -1;
}
pos += sign * a[i + 1];
if (prv.count(pos) && i != n - 1 && !(mask >> (i + 1) & 1)) {
cnt++;
}
cur.insert(pos);
}
ret = max(ret, cnt);
}
return ret;
}
signed main() {
#ifndef LOCAL
cin.tie(nullptr)->sync_with_stdio(false);
#endif // LOCAL
cin >> n;
for (int i = 1; i <= n; ++i) {
cin >> a[i];
a[i] += a[i - 1];
}
// cout << Brute() << '\n';
for (int j = 1; j <= n; ++j) {
for (int i = 0; i < j; ++i) {
f[i] = dp[i][j];
}
for (int i = 1; i < j; ++i) {
f[i] = max(f[i], f[i - 1]);
}
int cur = 0, cnt = 0;
for (int i = j - 1, k = j + 1; k <= n; ++k) {
dp[j][k] = cur;
while (i > 0 && a[i] + a[k] > a[j] * 2) {
i--;
}
if (i > 0 && a[i] + a[k] == a[j] * 2) {
cnt++;
cur = max(cur, f[i - 1] + cnt);
}
}
}
int ans = 0;
for (int i = 1; i <= n; ++i) {
ans = max(ans, dp[i][n]);
}
cout << ans << '\n';
#ifdef LOCAL
cerr << '\n' << clock() << "ms.";
#endif // LOCAL
return 0;
}
