include[HTML_REMOVED]

using namespace std;

define int long long

const int N = 1e5 + 10;
int n, a[N], b[N];

int exgcd(int a, int b, int &x, int &y) {
if(!b) {
x = 1, y = 0;
return a;
}

int d = exgcd(b, a % b, y, x);
y -= a / b * x;

return d;

}

int msc(int a, int b, int p) {
int ans = 0;
while(b) {
if(b & 1) ans = (ans + a) % p;
b >>= 1;
a = (a + a) % p;
}
return ans;
}

int excrt() {
int M = b[1], ans = a[1];
for(int i = 2; i <= n; i++) {
int x, y;
int c = ((a[i] - ans) % b[i] + b[i]) % b[i];
int g = exgcd(M, b[i], x, y);

    if(c % g) return -1;

    int t = b[i] / g;
    x = msc(x, c / g, t);
    ans += M * x;
    M *= t;
    ans = (ans % M + M) % M;
}
return ans;

}

signed main() {
cin >> n;
for(int i = 1; i <= n; i++) cin >> b[i] >> a[i]; //b是模数

cout << excrt();

return 0;

}