#include <algorithm>
#include <cstdint>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, s, t) for (int i = s; i < t; i++)
#define ALL(obj) obj.begin(), obj.end()

const int iINF = 1e9;
const long long llINF = 1e18;
const int MOD = 1e9 + 7;
template <class T>
inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}

template <int MOD>
struct ModInt {
    long long val;
    constexpr ModInt(long long v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr ModInt operator-() const noexcept { return val ? MOD - val : 0; }
    constexpr ModInt operator+(const ModInt& r) const noexcept { return ModInt(*this) += r; }
    constexpr ModInt operator-(const ModInt& r) const noexcept { return ModInt(*this) -= r; }
    constexpr ModInt operator*(const ModInt& r) const noexcept { return ModInt(*this) *= r; }
    constexpr ModInt operator/(const ModInt& r) const noexcept { return ModInt(*this) /= r; }
    constexpr ModInt& operator+=(const ModInt& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr ModInt& operator-=(const ModInt& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr ModInt& operator*=(const ModInt& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr ModInt& operator/=(const ModInt& r) noexcept {
        long long a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            long long t = a / b;
            a -= t * b;
            swap(a, b);
            u -= t * v;
            swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator==(const ModInt& r) const noexcept { return this->val == r.val; }
    constexpr bool operator!=(const ModInt& r) const noexcept { return this->val != r.val; }
    friend constexpr ostream& operator<<(ostream& os, const ModInt<MOD>& x) noexcept { return os << x.val; }

    friend constexpr istream& operator>>(istream& is, ModInt<MOD>& x) noexcept { return is >> x.val; }
    friend constexpr ModInt<MOD> modpow(const ModInt<MOD>& a, long long n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};

using mint = ModInt<MOD>;

long long modPow(long long x, long long n, long long mod) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * x % mod;
        x = x * x % mod;
        n >>= 1;
    }
    return res;
}

long long extGCD(long long a, long long b, long long& x, long long& y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }

    long long d = extGCD(b, a % b, y, x);
    y -= a / b * x;
    return d;
}

long long gcd(long long a, long long b) {
    if (b == 0) {
        return a;
    } else {
        return gcd(b, a % b);
    }
}

long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }

template <typename T>
map<T, int> compress(vector<T> x) {
    map<T, int> res;
    sort(x.begin(), x.end());
    x.erase(unique(x.begin(), x.end()), x.end());
    for (int i = 0; i < x.size(); i++) {
        res[x[i]] = i;
    }

    return res;
}

template <typename T>
int former(const vector<T>& v, T x) {
    return upper_bound(v.begin(), v.end(), x) - v.begin() - 1;
}

template <typename T>
int latter(const vector<T>& v, T x) {
    return lower_bound(v.begin(), v.end(), x) - v.begin();
}

template <class Monoid, class Action>
struct LazySegment {
    using FuncMonoid = function<Monoid(Monoid, Monoid)>;
    using FuncAction = function<Action(Action, Monoid)>;
    using FuncLazy = function<Action(Action, Action)>;

    FuncMonoid FM;
    FuncAction FA;
    FuncLazy FL;
    Monoid EM;
    Action EL;
    vector<Monoid> dat;
    vector<Action> lazy;
    int SIZE = 1;

    LazySegment(int n, const FuncMonoid fm, const FuncAction fa, const FuncLazy fl, const Monoid& em, const Action& el)
        : FM(fm), FA(fa), FL(fl), EM(em), EL(el) {
        while (SIZE < n) SIZE <<= 1;
        dat.assign(2 * SIZE - 1, em);
        lazy.assign(2 * SIZE - 1, el);

        for (int i = SIZE - 2; i >= 0; i--) {
            dat[i] = FM(dat[2 * i + 1], dat[2 * i + 2]);
        }
    }

    void set(int i, const Monoid& x) { dat[i + SIZE - 1] = x; }

    void eval(int k) {
        if (lazy[k] == EL) return;
        if (k < SIZE - 1) {
            lazy[k * 2 + 1] = FL(lazy[k * 2 + 1], lazy[k]);
            lazy[k * 2 + 2] = FL(lazy[k * 2 + 2], lazy[k]);
        }
        dat[k] = FA(dat[k], lazy[k]);
        lazy[k] = EL;
    }

    void update(int a, int b, const Monoid& x, int k = 0, int l = 0, int r = -1) {
        if (r < 0) r = SIZE;
        eval(k);
        if (b <= l || r <= a) return;

        if (a <= l && r <= b) {
            lazy[k] = FA(lazy[k], x);
            eval(k);
        } else {
            update(a, b, x, 2 * k + 1, l, (l + r) / 2);
            update(a, b, x, 2 * k + 2, (l + r) / 2, r);
            dat[k] = FM(dat[2 * k + 1], dat[2 * k + 2]);
        }
    }

    Monoid query(int a, int b, int k = 0, int l = 0, int r = -1) {
        if (r < 0) r = SIZE;
        eval(k);
        if (b <= l || r <= a) return EM;

        if (a <= l && r <= b) return dat[k];

        Monoid xl = query(a, b, 2 * k + 1, l, (l + r) / 2);
        Monoid xr = query(a, b, 2 * k + 2, (r + l) / 2, r);

        return FM(xl, xr);
    }

    void print() {
        for (int i = 0; i < SIZE; ++i) {
            cout << dat[i];
            if (i != SIZE) cout << ",";
        }
        cout << endl;
    }
};

template <typename T>
using Vec = vector<T>;
template <typename T>
using VVec = vector<vector<T>>;
using LL = long long;

LL dp[200010];
int main() {
    int N, M;
    cin >> N >> M;
    using Monoid = int;
    using Action = int;
    auto fm = [](Monoid a, Monoid b) -> Monoid { return max(a, b); };
    auto fa = [](Action a, Monoid m) -> Action { return m; };
    auto fl = [](Action a, Action b) -> Action { return b; };
    Monoid em = 0;
    Action el = 0;
    LazySegment<Monoid, Action> seg(N, fm, fa, fl, em, el);

    Vec<LL> A(N);
    Vec<pair<int, int>> v(M);
    REP(i, N) { cin >> A[i]; }
    REP(i, M) { cin >> v[i].second >> v[i].first; --v[i].second, --v[i].first;}
    sort(ALL(v));
    REP(i, N) { seg.update(i, i + 1, i + 1); }
    REP(i, M) { seg.update(v[i].second, v[i].first + 1, v[i].first + 1); }
    REP(i, N) {
        chmax(dp[i + 1], dp[i]);
        chmax(dp[seg.query(i, i + 1)], dp[i] + A[i]);
    }
    cout << dp[N] << endl;
}


Measured memory_bytes: 11524