#include<bits/stdc++.h>
#define ls i<<1
#define rs i<<1|1
#define fi first
#define se second
#define min amin
#define max amax
#define eb emplace_back
using namespace std;
using ll=long long;
using LL=__int128;
using pii=pair<int,int>;
const int N=1E5+10;
const int inf=0x3f3f3f3f;
const int p=998244353;
template<typename T=int>T read(){T x;cin>>x;return x;}
template<typename U,typename V>U min(const U &x,const V &y){return x<y?x:y;}
template<typename U,typename V>U max(const U &x,const V &y){return y<x?x:y;}
template<typename U,typename ...V>U min(const U &x,const V &...y){return min(x,min(y...));}
template<typename U,typename ...V>U max(const U &x,const V &...y){return max(x,max(y...));}
template<typename U,typename V>bool cmin(U &x,const V &y){return y<x?x=y,true:false;}
template<typename U,typename V>bool cmax(U &x,const V &y){return x<y?x=y,true:false;}
template<typename U,typename ...V>bool cmin(U &x,const V &...y){return cmin(x,min(y...));}
template<typename U,typename ...V>bool cmax(U &x,const V &...y){return cmax(x,max(y...));}
template<typename T>T qpow(T x,int n){T y=1;for(;n;n>>=1,x*=x)if(n&1)y*=x;return y;}
ll sqrt_floor(const ll &x){ll l=0,r=INT_MAX;while(l+1^r){ll mid=l+r>>1;(x<mid*mid?r:l)=mid;}return l;}
ll sqrt_ceil(const ll &x){ll l=-1,r=INT_MAX;while(l+1^r){ll mid=l+r>>1;(mid*mid<x?l:r)=mid;}return r;}
istream &operator>>(istream &is,LL &x){string a;is>>a;bool k=a[0]=='-';if(k)a=a.substr(1);x=0;for(char &t:a)x=x*10+t-48;if(k)x=-x;return is;}
ostream &operator<<(ostream &os,LL x){if(x<0)os<<'-',x=-x;string a;do a+=x%10|48;while(x/=10);reverse(a.begin(),a.end());return os<<a;}
mt19937 rng(time(0));
struct mint{
    int x;
    mint():x(){}
    mint(const int &x):x(x<0?x+p:x){}
    mint inv()const{return qpow(*this,p-2);}
    mint operator-()const{return mint(x?p-x:x);}
    mint &operator+=(const mint &t){return (x+=t.x)<p?0:x-=p,*this;}
    mint &operator-=(const mint &t){return (x-=t.x)<0?x+=p:0,*this;}
    mint &operator*=(const mint &t){return x=ll(x)*t.x%p,*this;}
    mint &operator/=(const mint &t){return *this*=t.inv();}
    mint operator+(const mint &t)const{return mint(*this)+=t;}
    mint operator-(const mint &t)const{return mint(*this)-=t;}
    mint operator*(const mint &t)const{return mint(*this)*=t;}
    mint operator/(const mint &t)const{return mint(*this)/=t;}
    friend mint operator+(const int &x,const mint &y){return mint(x)+=y;}
    friend mint operator-(const int &x,const mint &y){return mint(x)-=y;}
    friend mint operator*(const int &x,const mint &y){return mint(x)*=y;}
    friend mint operator/(const int &x,const mint &y){return mint(x)/=y;}
    friend istream &operator>>(istream &is,mint &t){return is>>t.x;}
    friend ostream &operator<<(ostream &os,const mint &t){return os<<t.x;}
};

int a[N],dp[N][4];
bool vis[N<<1];
void init(){
    int n=(N<<1)-1;
    for(int i=2;i<=n;++i)if(!vis[i]){
        for(int j=i<<1;j<=n;j+=i){
            vis[j]=true;
        }
    }
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    init();
    int n;
    cin>>n;
    for(int i=1;i<=n;++i){
        cin>>a[i];
    }
    dp[1][1]=dp[1][2]=dp[1][3]=1;
    for(int i=2;i<=n;++i){
        dp[i][0]=dp[i-1][2|a[i]&1];
        dp[i][1]=min(dp[i-1][1],dp[i-1][3]);
        dp[i][2]=dp[i-1][3];
        dp[i][3]=min(dp[i-1][1],dp[i-1][2]);
        if(!vis[a[i]+a[i-1]])cmin(dp[i][0],dp[i-1][0]);
        if(!vis[a[i]+1])cmin(dp[i][0],dp[i-1][1]);
        if(!vis[1+a[i-1]])cmin(dp[i][1],dp[i-1][0]);
        cmin(dp[i][2|a[i-1]&1],dp[i-1][0]);
        ++dp[i][1];
        ++dp[i][2];
        ++dp[i][3];
    }
    cout<<*min_element(dp[n],dp[n]+4)<<'\n';
    return 0;
}