#include #include #include #include #include #include #include #include #include typedef long long int ll; using namespace std; #define FOR(i,a,b) for (int i=(a);i<(b);i++) #define REP(i,n) for (int i=0;i<(n);i++) #define EREP(i,n) for (int i=1;i<=(n);i++) const int MOD = 1000000007; const int INF = 1000000; ll a,b,ans,M,temp; ll A[5010]; int N; int p,q; int main(){ scanf("%d",&N); REP(i,N)scanf("%lld",&A[i]); EREP(i,2*N-4){ REP(p,i+1){ int q=i-p; if(0<=p && pA[q]){ // cout<