神秘现象：不小心交了EXCTR结果过了几个样例

#include <bits/stdc++.h>
typedef __int128_t ll;
using namespace std;
ll a[100005], b[100005];

int read() {
    int ans = 0, f = 1;
    char c = getchar();
    while (!isdigit(c)) { if (c == '-') f = -1; c = getchar(); }
    while (isdigit(c)) { ans = (ans<<3) + (ans<<1) + (c-'0'); c = getchar(); }
    return f * ans;
}

void write(ll x) {
   static int sta[130];
   int top = 0;
   do {
       sta[top++] = x % 10;
       x /= 10;
   } while (x);
   while (top) putchar(sta[--top] + '0');
   putchar('\n');
}

ll exgcd(ll a, ll b, ll& x, ll& y) {
    if (b == 0) {
        x = 1, y = 0;
        return a;
    }
    ll ret = exgcd(b, a % b, x, y), z = x;
    x = y, y = z - (a / b) * y;
    return ret;
}

ll gcd(ll a, ll b) {
    if (b == 0) return a;
    return gcd(b, a % b);
    
}

int main () {
    ios::sync_with_stdio(false);
    cin.tie(nullptr), cout.tie(nullptr);
    ll n, m = 1, ans, M = 1;
    n = read();
    for (int i = 1; i <= n; ++i)
        a[i] = read(), b[i] = read();
    for (int i = 1; i <= n; ++i) {
        ll x, y;
        exgcd(m, a[i], x, y);
        ans = (ans + ((x * (b[i] - ans) / gcd(m, a[i])) * m) );
        m *= a[i] / gcd(m, a[i]);
    }
    write((ans % m + m) % m);
    return 0;
}