/*Author: Aayush Khazanchi                                   Date: 02/08/20
* 
* 
* */
import java.io.*;
import java.math.*;
import java.util.*;
public class Main{
	public static void main(String[] args) {  //Ball out dawg
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		int N = I.nextInt();
		long[] a = new long[N];
		long[] b = new long[N];
		long ans = 0;
		int in = N-1; //Last first and then proceed backwards
		//long pref = 0; //Cumulative sum = answer at the current time
		for (int i = 0; i < N; i++) {
			a[i] = I.nextLong();
			b[i] = I.nextLong();
		}
		while (in>=0) {
			a[in]+=ans;
			long curans = 0;
			if (a[in]<=b[in]&&a[in]>0) curans=b[in]-a[in]; 
			//If a[i] is 0, leaving it is best (edge case)
			//ZERO is a multiple of every number 
			else {
				long mod = a[in]%b[in];
				if (mod>0) curans=b[in]-mod; 
				//a[in]=9 and b[in]=4, modulo = 1; Therefore, 3 more steps to
				//NEXT multiple
			}
			//O.pln(curans);
			ans+=curans;
			in--;
		}
		O.pln(ans);
	}
	public static long min(long a, long b) {return Math.min(a,b);}
	public static int min(int a, int b) {return Math.min(a,b);}
	public static long max(long a, long b) {return Math.max(a,b);}
	public static long abs(long x, long y) {return Math.abs(x-y);}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return max(a,b);
		return GCD(max(a,b),max(a,b)%min(a,b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());};
		double nextDouble() {return Double.parseDouble(next());}
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	}
}


Measured memory_bytes: 48472