use std::cmp::*;
//use std::collections::*;
use std::io::*;
use std::str::FromStr;
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}
fn main(){
    let n:usize = read();
    let a:Vec<i64> = (0..n).map(|_| read()).collect();
    let mut minf:Vec<i64> = vec![10000000000;n];
    let mut minb:Vec<i64> = vec![10000000000;n];
    minf[0] = min(minf[0],a[0]);
    minb[n - 1] = min(minf[n - 1],a[n - 1]);
    for i in 1..n{
        minf[i] = min(minf[i - 1],a[i]);
        minb[n - 1 - i] = min(minb[n - i], a[n - 1 - i]);
    }
    let mut ans:i64 = 1e18 as i64;
    let mut cnt:i64 = 0;
    for i in 1..n - 1{
        if minf[i - 1] < a[i] && minb[i + 1] < a[i]{
            ans = min(ans,a[i]+minb[i + 1]+minf[i - 1]);
            cnt += 1;
        }
    }
    if cnt == 0 {
        ans = -1;
    }
    println!("{}",ans);
}