求助大佬！

#include <bits/stdc++.h>
using namespace std;
const int S = 1e7;
long long a[S], l[S], r[S]; 
int main() {
    long long n, sum = 0;
    scanf("%lld%lld", &n, &a[1]);
    for (int i = 2; i <= n; i++)
        a[i] = (a[i - 1] * 6807 + 2831) % 201701;
    for (int i = 1; i <= n; i++)
        l[i] = max(l[i - 1], a[i]);
    for (int i = n; i >= 1; i--)
        r[i] = max(r[i + 1], a[i]);
    for (int i = 1; i <= n; i++)
        sum += (min(l[i], r[i]) - a[i]);
    printf("%lld", sum);
    return 0;
}

哪里有错？