#include <cstdio>
#define MAXN 100010
using namespace std;
int N;
int v[MAXN];
int ext[MAXN];

int main(){
	
	freopen("numarare.in","r",stdin);
	freopen("numarare.out","w",stdout);

	scanf("%d",&N);
	
	int lval;
	
	scanf("%d",&lval);
	
	for (int i=1;i<N;++i){
		scanf("%d",&v[i]);
		int aux=v[i]; 
		
		v[i]=lval-v[i]; 
		lval=aux;
	}
	
	--N;
	
	if (N==0){
		
		printf("%d\n",0);
		fclose(stdout);
		return 0;
	}
	
	int npalis=1;
	int highint=1;
	int lowint=1;
	
	for (int i=2;i<=N;++i)
		if (i>highint){
			
			int clow=i-1;
			int chigh=i+1;
			
			while (clow>=1 && chigh<=N && v[clow]==v[chigh]){
				--clow;
				++chigh;
			}
			
			++clow;
			--chigh;
		
			ext[i]=i-clow+1;
			npalis+=ext[i];
			
			if (chigh>highint){
				highint=chigh;
				lowint=clow;
			}
		} else {
			
			int j=lowint-i+highint;
			
			ext[i]=ext[j];
			
			if (ext[i]>(highint-i+1)) ext[i]=highint-i+1;
			
			int clow=i-ext[i];
			int chigh=i+ext[i];
			
			while (clow>=1 && chigh<=N && v[clow]==v[chigh]){
				--clow;
				++chigh;
			}
			++clow;
			--chigh;
			
			ext[i]=i-clow+1;
			
			npalis+=ext[i];
			
			if (chigh>highint){
				highint=chigh;
				lowint=clow;
			}
		}
			
	
	printf("%d\n",npalis);
	
	fclose(stdout);
	
	return 0;
}