#include<cstdio>
#include<algorithm>
int a[200005];
int b[200005];
int c[200005][2];
int d[200005];
int map[200005];
int cnt[200005];

int min(int a,int b){ return a>b?b:a; }

void change(int p,int v,int n,int t){
    while(p<=n){
        c[p][t] += v;
        p += (p&-p);
    }
}

int ask(int p,int t){
    int res = 0;
    while(p!=0){
        res += c[p][t];
        p -= (p&-p);
    }
    return res;
}

int getId(int u,int n){
    int L = 1, R = n;
    int res = -1;
    while(L<=R){
        int M = (L+R)/2;
        if(map[M]<=u){
            res = M;
            L = M+1;
        }
        else R = M-1;
    }
    return res;
}

int preWork(int n){
    std::sort(d+1,d+1+n);
    int p = 1, size = 0;
    while(p<=n){
        int np = p;
        while(np+1<=n && d[np+1]==d[p]) np++;
        map[++size] = d[p];
        cnt[size] = np-p+1;
        p = np+1;
    }
    for(int i = 1; i <= size; i++){
        change(i,cnt[i],size,1);
    }
    return size;
}

int getBigger(int u,int n,int t){
    int L = u+1, R = n;
    int res = -1;
    int base = ask(u,t);
    while(L<=R){
        int M = (L+R)/2;
        if(ask(M,t)>base){
            res = M;
            R = M-1;
        }
        else L = M+1;
    }
    return res;
}

int solve(int n,int size){
    int minn = 1e9+7, ans = 1e9+7;
    for(int i = 2; i <= n-1; i++){
        minn = min(minn,a[i-1]);
        int last = getId(a[i-1],size);
        change(last,1,size,0);
        change(last,-1,size,1);
        int u = getId(a[i],size);
        if(minn<a[i]){
            int right = getBigger(getId(minn,size),size,1);
            if(right!=-1 && right<u) ans = min(ans,minn+a[i]+map[right]);
        }
        int left = getBigger(u,size,0), right = -1;
        if(left!=-1) right = getBigger(left,size,1);
        //printf("i = %d: l = %d, r = %d\n",i,left,right);
        //if(i==2) printf("%d %d\n",ask(2,0),ask(3,0));
        if(left!=-1 && right!=-1) ans = min(ans,map[left]+map[right]+a[i]);
    }
    return ans;
}

int main(){
    int n;
    scanf("%d",&n);
    for(int i = 1; i <= n; i++){ 
        scanf("%d",&a[i]);
        b[n-i+1] = a[i];
        d[i] = a[i];
    }
    int ans = 1e9+7;
    int size = preWork(n);
    ans = min(ans,solve(n,size));
    for(int i = 1;  i <= n; i++) a[i] = b[i];
    for(int i = 1; i <= 200000; i++) c[i][1] = c[i][0] = 0;
    for(int i = 1; i <= size; i++) change(i,cnt[i],size,1);
    ans = min(ans,solve(n,size));
    if(ans<1000000000) printf("%d\n",ans);
    else printf("-1\n");
    return 0;
}