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| #include<bits/stdc++.h>
#define ll long long
#define N 10010
#define fsb(a,b,c) for(int a=b;a<=c;a++)
#define fbs(a,b,c) for(int a=b;a>=c;a--)
using namespace std;
int a[N],n;
template<typename T>inline void rll(T &x){
T f=1;x=0;char c=getchar();
while(!isdigit(c))f=c=='-'?-1:f,c=getchar();
while(isdigit(c))x=x*10+c-'0',c=getchar();
x*=f;
}
inline int calc(int p,int x,int y){
if(p==0) return (x==0)?1:0;
int t=a[p]-x-y;
if(t<0||t>1)return 0;
return calc(p-1,t,x);
}
int main(){
rll(n);
fsb(i,1,n)rll(a[i]);
printf("%d\n",calc(n,0,0)+calc(n,1,0));
return 0;
}
|