#[doc = " https://github.com/hatoo/competitive-rust-snippets"]
#[allow(unused_imports)]
use std::cmp::{max, min, Ordering};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::iter::FromIterator;
#[macro_export]
macro_rules ! chmax { ( $ x : expr , $ ( $ v : expr ) ,+ ) => { $ ( $ x = std :: cmp :: max ( $ x ,$ v ) ; ) + } ; }
#[macro_export]
macro_rules ! chmin { ( $ x : expr , $ ( $ v : expr ) ,+ ) => { $ ( $ x = std :: cmp :: min ( $ x ,$ v ) ; ) + } ; }
#[macro_export]
macro_rules ! max { ( $ x : expr ) => ( $ x ) ; ( $ x : expr , $ ( $ xs : expr ) ,+ ) => { std :: cmp :: max ( $ x , max ! ( $ ( $ xs ) ,+ ) ) } ; }
#[macro_export]
macro_rules ! min { ( $ x : expr ) => ( $ x ) ; ( $ x : expr , $ ( $ xs : expr ) ,+ ) => { std :: cmp :: min ( $ x , min ! ( $ ( $ xs ) ,+ ) ) } ; }
#[macro_export]
macro_rules ! dvec { ( $ t : expr ; $ len : expr ) => { vec ! [ $ t ; $ len ] } ; ( $ t : expr ; $ len : expr , $ ( $ rest : expr ) ,* ) => { vec ! [ dvec ! ( $ t ; $ ( $ rest ) ,* ) ; $ len ] } ; }
#[macro_export]
macro_rules ! cfor { ( ; $ ( $ rest : tt ) * ) => { cfor ! ( ( ) ; $ ( $ rest ) * ) } ; ( $ ( $ init : stmt ) ,+; ; $ ( $ rest : tt ) * ) => { cfor ! ( $ ( $ init ) ,+; ! false ; $ ( $ rest ) * ) } ; ( $ ( $ init : stmt ) ,+; $ cond : expr ; ; $ body : block ) => { cfor ! { $ ( $ init ) ,+; $ cond ; ( ) ; $ body } } ; ( $ ( $ init : stmt ) ,+; $ cond : expr ; $ ( $ step : expr ) ,+; $ body : block ) => { { $ ( $ init ; ) + while $ cond { let mut _first = true ; let mut _continue = false ; loop { if ! _first { _continue = true ; break } _first = false ; $ body } if ! _continue { break } $ ( $ step ; ) + } } } ; }
#[doc = " main"]
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Write};
#[macro_export]
macro_rules ! input { ( source = $ s : expr , $ ( $ r : tt ) * ) => { let mut parser = Parser :: from_str ( $ s ) ; input_inner ! { parser , $ ( $ r ) * } } ; ( parser = $ parser : ident , $ ( $ r : tt ) * ) => { input_inner ! { $ parser , $ ( $ r ) * } } ; ( new_stdin_parser = $ parser : ident , $ ( $ r : tt ) * ) => { let stdin = std :: io :: stdin ( ) ; let reader = std :: io :: BufReader :: new ( stdin . lock ( ) ) ; let mut $ parser = Parser :: new ( reader ) ; input_inner ! { $ parser , $ ( $ r ) * } } ; ( $ ( $ r : tt ) * ) => { input ! { new_stdin_parser = parser , $ ( $ r ) * } } ; }
#[macro_export]
macro_rules ! input_inner { ( $ parser : ident ) => { } ; ( $ parser : ident , ) => { } ; ( $ parser : ident , $ var : ident : $ t : tt $ ( $ r : tt ) * ) => { let $ var = read_value ! ( $ parser , $ t ) ; input_inner ! { $ parser $ ( $ r ) * } } ; }
#[macro_export]
macro_rules ! read_value { ( $ parser : ident , ( $ ( $ t : tt ) ,* ) ) => { ( $ ( read_value ! ( $ parser , $ t ) ) ,* ) } ; ( $ parser : ident , [ $ t : tt ; $ len : expr ] ) => { ( 0 ..$ len ) . map ( | _ | read_value ! ( $ parser , $ t ) ) . collect ::< Vec < _ >> ( ) } ; ( $ parser : ident , chars ) => { read_value ! ( $ parser , String ) . chars ( ) . collect ::< Vec < char >> ( ) } ; ( $ parser : ident , usize1 ) => { read_value ! ( $ parser , usize ) - 1 } ; ( $ parser : ident , $ t : ty ) => { $ parser . next ::<$ t > ( ) . expect ( "Parse error" ) } ; }
use std::io;
use std::io::BufRead;
use std::str;
pub struct Parser<R> {
    reader: R,
    buf: Vec<u8>,
    pos: usize,
}
impl Parser<io::Empty> {
    pub fn from_str(s: &str) -> Parser<io::Empty> {
        Parser {
            reader: io::empty(),
            buf: s.as_bytes().to_vec(),
            pos: 0,
        }
    }
}
impl<R: BufRead> Parser<R> {
    pub fn new(reader: R) -> Parser<R> {
        Parser {
            reader: reader,
            buf: vec![],
            pos: 0,
        }
    }
    pub fn update_buf(&mut self) {
        self.buf.clear();
        self.pos = 0;
        loop {
            let (len, complete) = {
                let buf2 = self.reader.fill_buf().unwrap();
                self.buf.extend_from_slice(buf2);
                let len = buf2.len();
                if len == 0 {
                    break;
                }
                (len, buf2[len - 1] <= 0x20)
            };
            self.reader.consume(len);
            if complete {
                break;
            }
        }
    }
    pub fn next<T: str::FromStr>(&mut self) -> Result<T, T::Err> {
        loop {
            let mut begin = self.pos;
            while begin < self.buf.len() && (self.buf[begin] <= 0x20) {
                begin += 1;
            }
            let mut end = begin;
            while end < self.buf.len() && (self.buf[end] > 0x20) {
                end += 1;
            }
            if begin != self.buf.len() {
                self.pos = end;
                return str::from_utf8(&self.buf[begin..end]).unwrap().parse::<T>();
            } else {
                self.update_buf();
            }
        }
    }
}
#[allow(unused_macros)]
macro_rules ! debug { ( $ ( $ a : expr ) ,* ) => { eprintln ! ( concat ! ( $ ( stringify ! ( $ a ) , " = {:?}, " ) ,* ) , $ ( $ a ) ,* ) ; } }
#[doc = " https://github.com/hatoo/competitive-rust-snippets"]
const BIG_STACK_SIZE: bool = true;
#[allow(dead_code)]
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}
fn solve() {
    let out = stdout();
    let mut out = BufWriter::new(out.lock());
    input!{
        n:usize,m:usize,
        a:[i64;n],
        xw:[(usize,i64);m],
    }

    // c=infでもだめか？
    let mut rem = a.clone();
    for i in 0..m {
        let (x,w) = xw[i];
        let x = x-1;
        rem[x] -= w;
    }
    let mut ok = true;
    for i in 0..n {
        if rem[i] <= 0 {
            ok = false;
        }
    }
    if !ok {
        writeln!(out,"-1");
        return
    }

    // c=0でおっけーか？
    let mut tot = 0;
    for i in 0..m {
        tot += xw[i].1;
    }
    let mut ok = true;
    for i in 0..n {
        if tot >= a[i] {
            ok = false
        }
    }
    if ok {
        writeln!(out,"0");
        return
    }

    let qu = |c:i64| {
        let mut imos = Imosu1d::new(n);
        for i in 0..m {
            let (x,w) = xw[i];
            let x = x-1;
            let leftline = ArithSeq::from_point(x as i64, w, c);
            let r = max(0, leftline.lower_bound(0)) as usize;
            imos.add_line(r, x, leftline);
            let rightline = ArithSeq::from_point(x as i64, w, -c);
            let r = min(n as i64, rightline.lower_bound(0)) as usize;
            imos.add_line(x, r, rightline);
        }
        imos.build();
        let mut ok = true;
        for i in 0..n {
            let sum = imos.get(i);
            if sum >= a[i] {
                ok = false;
            }
        }
        ok
    };
    let mut bs = BinarySearch {
        lower: 1,
        upper: 1<<40,
        p: qu,
    };
    let r = bs.lower_bound();
    writeln!(out,"{}",r);
}
pub struct ArithSeq {
    pub a: i64,
    pub b: i64,
}
impl ArithSeq {
    #[doc = "y=ax+b"]
    pub fn new(a: i64, b: i64) -> Self {
        ArithSeq { a: a, b: b }
    }
    pub fn from_point(x0: i64, y0: i64, a: i64) -> Self {
        let b = y0 - a * x0;
        Self::new(a, b)
    }
    pub fn y(&self, x: i64) -> i64 {
        self.a * x + self.b
    }
    #[doc = "x such that f(x) >= y and f(x-1) < y"]
    pub fn lower_bound(&self, y: i64) -> i64 {
        assert!(self.a != 0);
        let a = self.a;
        let b = self.b;
        if a > 0 {
            let mut x = y - b;
            if x >= 0 {
                x += a - 1;
            } else {
            }
            let x = x / a;
            x
        } else {
            let y = 2 * b - y;
            let mirror = Self::new(-a, b);
            mirror.lower_bound(y)
        }
    }
    #[doc = "x such that f(x) < y and f(x+1) >= y"]
    pub fn upper_bound(&self, y: i64) -> i64 {
        unimplemented!()
    }
}
struct Imosu1d {
    n: usize,
    dp1: Vec<i64>,
    dp2: Vec<i64>,
    dp3: Vec<i64>,
}
impl Imosu1d {
    pub fn new(n: usize) -> Imosu1d {
        Imosu1d {
            n: n,
            dp1: vec![0;n+1],
            dp2: vec![0;n+1],
            dp3: vec![0;n+1],
        }
    }
    #[doc = "y=ax+b"]
    pub fn add_line(&mut self, l: usize, r: usize, line: ArithSeq) {
        if l >= r { return; }

        let a = line.a;
        let b = line.b;

        let y = line.y(l as i64);
        self.dp1[l] += y;
        self.dp1[r] += -y;

        self.dp2[l+1] += a;
        self.dp2[r] += -a;

        let L = r - (l+1);
        self.dp3[r] += -a * L as i64;
    }
    pub fn get(&self, k: usize) -> i64 {
        self.dp1[k]
    }
    fn sweep(dp: &mut [i64]) {
        let mut cur = 0;
        for i in 0..dp.len() {
            cur += dp[i];
            dp[i] = cur;
        }
    }
    pub fn build(&mut self) {
        let n = self.dp1.len();
        Self::sweep(&mut self.dp1);
        Self::sweep(&mut self.dp2);
        for i in 0..n {
            self.dp2[i] += self.dp3[i];
        }
        Self::sweep(&mut self.dp2);
        for i in 0..n {
            self.dp1[i] += self.dp2[i];
        }
    }
}
#[doc = "lower,upper are inclusive range"]
pub struct BinarySearch<F> {
    pub p: F,
    pub lower: i64,
    pub upper: i64,
}
impl<F: FnMut(i64) -> bool> BinarySearch<F> {
    #[doc = "O(log(upper-lower))"]
    pub fn lower_bound(&mut self) -> i64 {
        let lower = self.lower;
        let upper = self.upper;
        assert!(lower <= upper);
        let mut lb = lower - 1;
        let mut ub = upper + 1;
        while ub - lb > 1 {
            let mid = (lb + ub) / 2;
            let ok = (self.p)(mid);
            if ok {
                ub = mid;
            } else {
                lb = mid;
            }
        }
        ub
    }
}