let Mod = 1000000007

func power(base a: Int, exponent b: Int) -> Int {
    if b == 0 {
        return 1
    }
    
    if b == 1 {
        return a
    }
    
    var half = power(base: a, exponent: b/2)
    half = (half * half) % Mod
    
    if b%2 == 1 {
        return (a * half) % Mod
    }
    else {
        return half
    }
}

func gcd(_ x: Int, _ y: Int) -> Int {
    var a = max(x,y)
    var b = min(x,y)
    
    while b != 0 {
        let r = a%b
        a = b
        b = r
    }
    
    return a
}

if let M = Int(readLine() ?? "") {
    var result = 0
    
    for _ in 0..<M {
        if let input = readLine(),
           let info = input.split(separator: " ").compactMap({Int($0)}) as? [Int],
           info.count == 2
        {
            var N = info[0]
            var S = info[1]
            
            let GCD = gcd(N, S)
            N /= GCD
            S /= GCD
            
            result += S*(power(base: N, exponent: Mod-2))%Mod
            result %= Mod
        }
    }
    
    print(result)
}