题解

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#include <iostream>
#include <vector>
using namespace std;

const int MAX = 2000000;
vector<bool> light(MAX + 5, false);

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    cin >> n;
    while (n--)
    {
        double a;
        int t;
        cin >> a >> t;
        for (int k = 1; k <= t; ++k)
        {
            int id = (int)(a * k);
            light[id] = !light[id];
        }
    }
    
    for (int i = 1; i <= MAX; ++i)
    {
        if (light[i])
        {
            cout << i << endl;
            break;
        }
    }
    return 0;
}