#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 5;

long long a[N], b[N];

int main() {
#ifdef HOME_NONU
    freopen("dat.in", "r", stdin);
    freopen("dat.out", "w", stdout);
#endif
    long long n, ans = 0;
    scanf("%lld", &n);
    for (int i = 1; i <= n; i++)
        scanf("%lld %lld", &a[i], &b[i]);
    for (int i = n; i >= 1; i--) {
        if ((a[i] + ans) % b[i] > 0) {
            ans = ans + b[i] - (a[i] + ans) % b[i]; } }
    printf("%lld\n", ans);
    return 0; }