//#pragma GCC optimize(1)
//#pragma GCC optimize(2)
//#pragma GCC optimize(3, "Ofast", "inline")

#include <bits/stdc++.h>

#define int long long
#define ld long double
#define i32 int
#define u32 unsigned int
#define i64 long long
#define u64 unsigned long long
#define u27 __int128
#define endl '\n'
#define VI vector<int>
#define VVI vector<VI>
#define rand() RANDOM(GEN)
#define IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define CTM (cout<<"Time:"<<static_cast<double>(clock()-START_TIME)/CLOCKS_PER_SEC*1000<<"ms"<<endl)
typedef long long ll;

using namespace std;
random_device SEED;
mt19937_64 GEN(SEED());
uniform_int_distribution<u64> RANDOM(0, numeric_limits<u64>::max());
const clock_t START_TIME = clock();
const int N=1e5+50,M=2e5;
bool f[M+50];
int sz[N],dp[N][3];
signed main() {
#ifndef ONLINE_JUDGE
    freopen(".in", "r", stdin);
    freopen(".out", "w", stdout);
#endif
    IO;
    for (int i = 2; i <= M; ++i) {
        for (int j = 2*i; j <= M; j+=i) {
            f[j]=1;
        }
    }
    int n;
    cin>>n;
    for (int i = 1; i <= n; ++i) {
        cin>>sz[i];
    }
    memset(dp,127,sizeof(dp));
    dp[1][0]=0,dp[1][1]=dp[1][2]=1;
    for (int i = 2; i <= n; ++i) {
        for (int j = 0; j < 3; ++j) {
            if(!f[sz[i]+sz[i-1]]) {
                dp[i][0]=min(dp[i][0],dp[i-1][0]);
            }
            if(!f[1+sz[i-1]]) {
                dp[i][1]=min(dp[i][1],dp[i-1][0]+1);
            }
            if(!f[2+sz[i-1]]) {
                dp[i][2]=min(dp[i][2],dp[i-1][0]+1);
            }
            if(!f[1+sz[i]]) {
                dp[i][0]=min(dp[i][0],dp[i-1][1]);
            }
            if(!f[2+sz[i]]) {
                dp[i][0]=min(dp[i][0],dp[i-1][2]);
            }
            dp[i][1]=min({dp[i][1],dp[i-1][1]+1,dp[i-1][2]+1});
            dp[i][2]=min({dp[i][2],dp[i-1][1]+1});
        }
    }
    cout<<min({dp[n][0],dp[n][1],dp[n][2]});
    return 0;
}