import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop, core.stdc.string;

immutable long INF = 1L<<59;

void main() {
    auto s = readln.split.map!(to!int);
    auto N = s[0];
    auto M = s[1];
    auto LRA = M.iota.map!(_ => readln.split.map!(to!int).array).array;
    LRA.sort();

    auto st = new LazySegmentTree!(long, long, max, (a,b)=>a+b, (a,b)=>a+b, (a,b)=>a, -INF, 0L)(N+2);
    st.table[] = 0L;
    auto pq = new BinaryHeap!(Array!(Tuple!(int, int, long)), "a[1] > b[1]")();

    for (int i = 1, p = 0; i <= N+1; ++i) {
        while (p < M && i >= LRA[p][0]) {
            pq.insert(tuple(LRA[p][0], LRA[p][1], LRA[p][2].to!long));
            st.update(0, LRA[p][0]-1, LRA[p][2].to!long);
            ++p;
        }
        while (!pq.empty && pq.front[1] < i) {
            st.update(0, pq.front[0]-1, -pq.front[2].to!long);
            pq.removeFront;
        }

        auto v = st.query(0, i-1);
        st.update(i, i, v);
    }

    st.query(N+1, N+1).writeln;
}



class LazySegmentTree(T, L, alias opTT, alias opTL, alias opLL, alias opPrd, T eT, L eL) {
    T[] table;
    L[] lazy_;
    int n;
    int size;

    this(int n) {
        this.n = n;
        size = 1;
        while (size <= n) size <<= 1;
        size <<= 1;
        table = new T[](size);
        lazy_ = new T[](size);
        table[] = eT;
        lazy_[] = eL;
    }

    void push(int i, int a, int b) {
        if (lazy_[i] == eL) return;
        table[i] = opTL(table[i], opPrd(lazy_[i], b - a + 1));
        if (i * 2 + 1 < size) {
            lazy_[i*2] = opLL(lazy_[i*2], lazy_[i]);
            lazy_[i*2+1] = opLL(lazy_[i*2+1], lazy_[i]);
        }
        lazy_[i] = eL;
    }

    T query(int l, int r) {
        if (l > r) return eT;
        return query(l, r, 1, 0, n-1);
    }

    T query(int l, int r, int i, int a, int b) {
        if (b < l || r < a) return eT;
        push(i, a, b);
        if (l <= a && b <= r) {
            return table[i];
        } else {
            return opTT(query(l, r, i*2, a, (a+b)/2), query(l, r, i*2+1, (a+b)/2+1, b));
        }
    }

    void update(int l, int r, L val) {
        if (l > r) return;
        update(l, r, 1, 0, n-1, val);
    }

    void update(int l, int r, int i, int a, int b, L val) {
        if (b < l || r < a) {
            push(i, a, b);
        } else if (l <= a && b <= r) {
            lazy_[i] = opLL(lazy_[i], val);
            push(i, a, b);
        } else {
            push(i, a, b);
            update(l, r, i*2, a, (a+b)/2, val);
            update(l, r, i*2+1, (a+b)/2+1, b, val);
            table[i] = opTT(table[i*2], table[i*2+1]);
        }
    }
}
