代码：

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long uLL;
void fast_io();
const int MAXN = 1e5+5;
int n;
LL a[MAXN],b[MAXN];
LL mod(LL a, LL b);
LL lcm(LL a, LL b);
void exgcd(LL a, LL b, LL &x, LL &y);
LL excrt() {
    LL d, p1, p2, lambda1, lambda2;
    b[0] = mod(b[0], a[0]);
    for (int i = 0; i < n - 1; i++)
    {
        d = __gcd(a[i], a[i + 1]);
        p1 = a[i] / d;
        p2 = a[i + 1] / d;
        exgcd(p1, p2, lambda1, lambda2);
        b[i + 1] = b[i] + (b[i + 1] - b[i]) / d * lambda1 * a[i];
        a[i + 1] = lcm(a[i], a[i + 1]);
        b[i + 1] = mod(b[i + 1], a[i + 1]);
    }
    return b[n - 1];
}
int main() {
    fast_io();
    cin>>n;
    for (int i = 0; i < n; i++)
        cin>>a[i]>>b[i];
    cout<<excrt();
    return 0;
}

void fast_io() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
}

LL mod(LL a, LL b) {
    return (a%b+b)%b;
}

LL lcm(LL a, LL b) {
    return a/__gcd(a, b)*b;
}

void exgcd(LL a, LL b, LL &x, LL &y) { //求解 ax+by=gcd(a,b)
    if (b == 0) {
        x = 1;
        y = 0;
        return;
    }
    exgcd(b, a % b, y, x);
    y -= a / b * x;
}

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