为什么最后一个点会RE啊？

#include<bits/stdc++.h>
using namespace std;
int minn = 1e9;
int x, y, z;
#define MAXN 100005
int n, p;
int a[MAXN],b[MAXN];
int main() {
	cin >> n >> p;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	for (int i = 1; i <= n; i++) {
		b[i] = a[i] - a[i - 1];
	}
	for (int i = 0; i < p; i++) {
		cin >> x >> y >> z;
		b[x] += z, b[y + 1] -= z;
	}
	for (int i = 1; i <= n; i++) {
		a[i] = a[i - 1] + b[i];
		if(minn > a[i]) minn = a[i];
	}
	cout << minn;
	return 0;
}