80求助

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;
}