export {};
const input = require("fs").readFileSync(0).toString().trim().split('\n');
const MOD = BigInt(1000000007);

const power = (num: bigint, n: bigint): bigint => {
    if(n===BigInt(0)) return BigInt(1);
    else if(n===BigInt(1)) return num%MOD;

    const half = power(num, n/BigInt(2));
    let result = (half * half) % MOD;

    if(n%BigInt(2) === BigInt(1)) result = (result*num)%MOD;

    return result;
}

let result = BigInt(0);

for(let line of input.slice(1)) {
    const [N, S] = line.split(" ").map(BigInt);

    result = (result + (S * power(N, MOD - BigInt(2))) % MOD) % MOD;
}

console.log(result.toString());