/* 全く分からない */

package no187a;

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;

public class Main {
	static long MOD = 1000000007;
	static IO io = new IO();
	public static void main(String[] args) {
		int n = io.nextInt();
		BigInteger[] a = new BigInteger[n];
		BigInteger[] b = new BigInteger[n];
		BigInteger[] m = new BigInteger[n];
		for(int i=0;i<n;i++) {
			a[i] = BigInteger.ONE;
			b[i] = new BigInteger(io.next());
			m[i] = new BigInteger(io.next());
		}
		BigInteger[] x = Mod.linearCongruence(a, b, m);
		if (x == null) {
			System.out.println(-1);
		}else if(x[0].equals(BigInteger.ZERO)) {
			if (x[1].signum() > 0) {
				System.out.println(x[1]);
			}else{
				System.out.println(-1);
			}
		}else{
			System.out.println((x[0].remainder(x[1]).add(x[1])).remainder(x[1]));
		}
	}
}
class Mod {
	public static BigInteger[] linearCongruence(BigInteger[] A,BigInteger[] B,BigInteger[] M) {
		BigInteger x = BigInteger.ZERO;
		BigInteger m = BigInteger.ONE;
		for(int i=0;i<A.length;i++) {
			BigInteger a = A[i].multiply(m);
			BigInteger b = B[i].subtract(A[i].multiply(x));
			BigInteger d = M[i].gcd(a);
			if (!b.remainder(d).equals(BigInteger.ZERO)) {
				return null;
			}
			BigInteger t = b.divide(d).multiply(a.divide(d).modInverse(M[i].divide(d)).remainder(M[i].divide(d)));
			x = x.add(m.multiply(t));
			m = m.multiply(M[i]).divide(d);
		}
		BigInteger[] ret = {x.remainder(m), m};
		return ret;
	}
}
class IO extends PrintWriter {
	private final InputStream in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	public IO() { this(System.in);}
	public IO(InputStream source) { super(System.out); this.in = source;}
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		}else{
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}
	private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
	private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
	private static boolean isNewLine(int c) { return c == '\n' || c == '\r';}
	public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
	public boolean hasNextLine() { while(hasNextByte() && isNewLine(buffer[ptr])) ptr++; return hasNextByte();}
	public String next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while(isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	public char[] nextCharArray(int len) {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		char[] s = new char[len];
		int i = 0;
		int b = readByte();
		while(isPrintableChar(b)) {
			if (i == len) {
				throw new InputMismatchException();
			}
			s[i++] = (char) b;
			b = readByte();
		}
		return s;
	}
	public String nextLine() {
		if (!hasNextLine()) {
			throw new NoSuchElementException();
		}
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while(!isNewLine(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	public long nextLong() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while(true){
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			}else if(b == -1 || !isPrintableChar(b)){
				return minus ? -n : n;
			}else{
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) {
			throw new NumberFormatException();
		}
		return (int) nl;
	}
	public char nextChar() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		return (char) readByte();
	}
	public double nextDouble() { return Double.parseDouble(next());}
	public int[] nextIntArray(int n) { int[] a = new int[n]; for(int i=0;i<n;i++) a[i] = nextInt(); return a;}
	public long[] nextLongArray(int n) { long[] a = new long[n]; for(int i=0;i<n;i++) a[i] = nextLong(); return a;}
	public double[] nextDoubleArray(int n) { double[] a = new double[n]; for(int i=0;i<n;i++) a[i] = nextDouble(); return a;}
	public void nextIntArrays(int[]... a) { for(int i=0;i<a[0].length;i++) for(int j=0;j<a.length;j++) a[j][i] = nextInt();}
	public int[][] nextIntMatrix(int n,int m) { int[][] a = new int[n][]; for(int i=0;i<n;i++) a[i] = nextIntArray(m); return a;}
	public char[][] nextCharMap(int n,int m) { char[][] a = new char[n][]; for(int i=0;i<n;i++) a[i] = nextCharArray(m); return a;}
	public void close() { super.close(); try {in.close();} catch (IOException e) {}}
}