int size_ = 1;

vector<long long> dat;

void init(int sz) {

while (size_ <= sz) size_ *= 2;

dat.resize(size_ * 2, -(1LL << 60));

}

void update(int pos, long long x) {

pos += size_;

dat[pos] = x;

while (pos >= 2) {

pos >>= 1;

dat[pos] = max(dat[pos * 2], dat[pos * 2 + 1]);

}

}

long long query_(int l, int r, int a, int b, int u) {

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

if (r <= a || b <= l) return -(1LL << 60);

long long v1 = query_(l, r, a, (a + b) >> 1, u * 2);

long long v2 = query_(l, r, (a + b) >> 1, b, u * 2 + 1);

return max(v1, v2);

}

long long query(int l, int r) {

return query_(l, r, 0, size_, 1);

}

// Step #1. 入力

cin >> W >> N;

for (int i = 1; i <= N; i++) cin >> L[i] >> R[i] >> V[i];

// Step #2. 初期化

for (int i = 0; i <= N; i++) {

for (int j = 0; j <= W; j++) dp[i][j] = -(1LL << 60);

Z[i].init(W + 2);

}

dp[0][0] = 0;

Z[0].update(0, 0);

// Step #3. 動的計画法

for (int i = 1; i <= N; i++) {

for (int j = 0; j <= W; j++) dp[i][j] = dp[i - 1][j];

for (int j = 0; j <= W; j++) {

int cl = max(0, j - (int)R[i]), cr = max(0, j - (int)L[i] + 1);

if (cl == cr) continue;

long long val = Z[i - 1].query(cl, cr);

if (val != -(1LL << 60)) {

dp[i][j] = max(dp[i][j], val + V[i]);

}

}

for (int j = 0; j <= W; j++) Z[i].update(j, dp[i][j]);

}

// Step #4. 出力

if (dp[N][W] == -(1LL << 60)) cout << "-1" << endl;

else cout << dp[N][W] << endl;

return 0;

}