//{{{
#include <bits/stdc++.h>
using namespace std;

#define putchar(x) cout << (x)
#define repeat(x) int _ = 0; _ < (x); ++_

template<typename T> constexpr auto range(T start, T stop, T step) {
    struct iterator {
        T i, step;
        bool operator!=(const iterator& other) const { return i != other.i; }
        auto& operator++() { i += step; return *this; }
        auto& operator*() { return i; }
    };
    struct iterable_wrapper {
        T start, stop, step;
        auto begin() const { return iterator{ start, step }; }
        auto end() const { return iterator{ stop, step }; }
        size_t size() const { return (stop - start) / step; }

        iterable_wrapper(T start_, T stop_, T step_): start(start_), stop(stop_), step(step_) {
            stop = step > 0 ? max(start, stop) : min(start, stop);
            stop += (step - (stop - start) % step) % step;
        }
    };
    return iterable_wrapper(start, stop, step);
};
template<typename T> constexpr auto range(T start, T stop) { return range(start, stop, T(1)); }
template<typename T> constexpr auto range(T stop) { return range(T(0), stop, T(1)); }

template<typename T, typename Iter = decltype(begin(declval<T>()))>
constexpr auto printer(T&& iterable) {
    struct iterator {
        Iter iter, ed;
        auto operator!=(const iterator& other) const {
            auto ret = (iter != other.iter);
            if(not ret) cout << '\n';
            return ret;
        }
        auto& operator++() { ++iter; if(iter != ed) cout << ' '; return *this; }
        auto& operator*() { return *iter; }
    };
    struct iterable_wrapper {
        T iterable;
        auto begin() const { return iterator{ std::begin(iterable), std::end(iterable) }; }
        auto end() const { return iterator{ std::end(iterable), std::end(iterable) }; }
    };
    return iterable_wrapper{ forward<T>(iterable) };
};

template<size_t ...Is, typename T> auto getis(const T& t) { return tie(get<Is>(t)...); }
template<class T> void setmax(T& a, const T& b) { a = max(a, b); }
template<class T> void setmin(T& a, const T& b) { a = min(a, b); }

template<typename T> struct is_const_char_arr_ref : false_type {};
template<size_t N> struct is_const_char_arr_ref<char const (&)[N]> : true_type {};
template<typename T, typename = void> struct is_container : false_type {};
template<typename T>
struct is_container<T, conditional_t<false, decltype(begin(declval<T>())), void>> : true_type {};
template<class T> using IsC = typename enable_if<is_container<T>::value and
    not is_same<T, string>::value>::type;
template<class T> using NotC = typename enable_if<not is_container<T>::value or
    is_same<T, string>::value>::type;
template<class T> inline IsC<T> print_1(const T& v);
template<class T> inline NotC<T> print_1(const T& x) { cout << x; }
template<size_t N> void print_1(const array<char, N>& x) { cout << &x[0]; };
inline void print_1(const tuple<>&) { cout << "()"; };
template<size_t L, size_t I, class T> void print_tuple(const T& t) {
    if(I != 0) cout << ", "; print_1(get<I>(t));
    if(I + 1 < L) print_tuple<L, (I + 1) % L>(t);
}
template<class ...T> inline void print_1(const tuple<T...>& x) {
    cout << "("; print_tuple<sizeof...(T), 0, tuple<T...>>(x); cout << ")";
}
inline void print_n() {}
template<class T, class ...U> inline void print_n(const T& head, const U&... tail);
template<class T, class U> inline void print_1(const pair<T, U>& p) {
    cout << "("; print_1(p.first); cout << ", "; print_1(p.second); cout << ")";
}
template<class T, class ...U> inline void print_n(const T& head, const U&... tail) {
    print_1(head); if(sizeof...(tail)) cout << " "; print_n(tail...);
}
template<class T> inline IsC<T> print_1(const T& v) {
    cout << "[";
    for(auto it = v.begin(); it != v.end(); ++it) { if(it != v.begin()) cout << ", "; print_1(*it); }
    cout << "]";
}
template<class ...T> inline void print(const T& ...args) { print_n(args...); putchar('\n'); }
inline void read() {}
template<class T, class ...U> inline void read(T& head, U&... tail) { cin >> head; read(tail...); }

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
static int fastio = [](){ ios_base::sync_with_stdio(false); cin.tie(0); cout.precision(17); return 0; }();

template<class T> void print_dbg(const string& s, T&& x) {
    if(is_const_char_arr_ref<T>::value) { print_n(x); } else { print_n(s, "=", x); }
}
#define SELECT(_1, _2, _3, _4, _5, _6, _7, _8, NAME,...) NAME
#define dbg1(a) print_dbg(#a, a); cout << endl;
#define dbg2(a, b) print_dbg(#a, a); cout << ", "; dbg1(b);
#define dbg3(a, b, c) print_dbg(#a, a); cout << ", "; dbg2(b, c);
#define dbg4(a, b, c, d) print_dbg(#a, a); cout << ", "; dbg3(b, c, d);
#define dbg5(a, b, c, d, e) print_dbg(#a, a); cout << ", "; dbg4(b, c, d, e);
#define dbg6(a, b, c, d, e, f) print_dbg(#a, a); cout << ", "; dbg5(b, c, d, e, f);
#define dbg7(a, b, c, d, e, f, g) print_dbg(#a, a); cout << ", "; dbg6(b, c, d, e, f, g);
#define dbg8(a, b, c, d, e, f, g, h) print_dbg(#a, a); cout << ", "; dbg7(b, c, d, e, f, g, h);
#define debug(...) SELECT(__VA_ARGS__, dbg8, dbg7, dbg6, dbg5, dbg4, dbg3, dbg2, dbg1)(__VA_ARGS__)
//}}}
using PII = pair<int, int>;
using LL = long long;

const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const LL LLINF = 0x3f3f3f3f3f3f3f3f;
const int MAX_N = 200005;

using Data = LL;
vector<Data> dat, lazy;

const Data zero_m = 0, zero_c = -LLINF;

Data modify(const Data& val1, const Data& val2, int = 1) {
    return val1 + val2;
}
Data combine(const Data& val1, const Data& val2) {
    return max(val1, val2);
}

struct SegTree {//{{{
    int N;
    SegTree(int n_, Data *a = NULL) {
        N = 1;
        while(N < n_) {
            N <<= 1;
        }
        dat.assign(N * 2, 0);
        lazy.assign(N * 2, zero_m);

        if(a != NULL) {
            for(int i = 0; i < n_; i++) dat[i + N] = a[i];
            for(int k = N - 1; k >= 0; k--) {
                dat[k] = combine(dat[k << 1], dat[k << 1 | 1]);
            }
        }
    }

    void pull(int k, int l, int r) {
        int lc = (k << 1), rc = (k << 1) | 1;
        dat[k] = combine(
            modify(dat[lc], lazy[lc], (r - l) / 2),
            modify(dat[rc], lazy[rc], (r - l) / 2)
        );
    }

    void push(int k, int l, int r) {
        int lc = (k << 1), rc = (k << 1) | 1;
        if(lazy[k] != zero_m) {
            dat[k] = modify(dat[k], lazy[k], r - l);
            if(l != r - 1) {
                lazy[lc] = modify(lazy[lc], lazy[k]);
                lazy[rc] = modify(lazy[rc], lazy[k]);
            }
            lazy[k] = zero_m;
        }
    }

    void update(int a, const Data& val, int l = 0, int r = -1, int k = 1) {
        r = (r < 0)? N : r;

        if(r <= a or a < l) {
            return;
        }
        if(l == r - 1) {
            dat[k] = modify(dat[k], val);
            return;
        }
        int mid = l + (r - l) / 2;
        push(k, l, r);
        update(a, val, l, mid, k << 1);
        update(a, val, mid, r, k << 1 | 1);
        pull(k, l, r);
    }

    void update_range(int a, int b, const Data& val, int l = 0, int r = -1, int k = 1) {
        r = (r < 0)? N : r;

        if(r <= a or b <= l) {
            return;
        }
        if(a <= l and r <= b) {
            lazy[k] = modify(lazy[k], val);
            push(k, l, r);
            return;
        }

        int mid = l + (r - l) / 2;
        push(k, l, r);
        update_range(a, b, val, l, mid, k << 1);
        update_range(a, b, val, mid, r, k << 1 | 1);
        pull(k, l, r);
    }

    Data query(int a, int b, int l = 0, int r = -1, int k = 1) {
        r = (r < 0)? N : r;

        if(r <= a or b <= l) {
            return zero_c;
        }
        push(k, l, r);

        if(a <= l and r <= b) {
            return dat[k];
        }
        int mid = l + (r - l) / 2;
        Data vl = query(a, b, l, mid, k << 1);
        Data vr = query(a, b, mid, r, k << 1 | 1);
        return combine(vl, vr);
    }
};//}}}

struct Solution {
    Solution(int) {
        int N, M;
        read(N, M);
        vector<vector<pair<int, LL>>> ls(N + 2), rs(N + 2);
        for(repeat(M)) {
            int l, r, a;
            read(l, r, a);
            ++r;
            ls[l].emplace_back(l, a);
            rs[r].emplace_back(l, a);
        }
        auto st = SegTree(N + 2);

        LL ans = 0;
        vector<LL> dp(N + 1);
        for(int i : range(1, N + 1)) {
            LL l, a;
            for(auto& p : rs[i]) {
                tie(l, a) = p;
                st.update_range(0, l, -a);
            }
            for(auto& p : ls[i]) {
                tie(l, a) = p;
                st.update_range(0, l, a);
            }

            dp[i] = st.query(0, i);
            setmax(ans, dp[i]);
            st.update(i, dp[i]);
        }
        print(ans);
    }
};

int main() {
    int T = 1;
    //cin >> T;
    for(int i = 1; i <= T; ++i) {
        ignore = Solution(i);
    }
    return 0;
}


Measured memory_bytes: 32000