用两分怎么不行啊

#include<bits/stdc++.h>
using namespace std;
typedef long long i64;
typedef long long ll;
int _T = 1, MOD = 1e9 + 7;
void solve(){
    ll a, b, c, d;
    cin >> a >> b >> c >> d;
    ll l = 0,r = 1e10;
    ll lcm = b*d/__gcd(b,d);
    while(l < r) {
        ll k = l + (r - l)/2;
        if(k * lcm/b < c * lcm/d) l = k + 1;
        else r = k;
    }
    cout << a - (l - 1) << ' ';
}
int main() {
    cin >> _T;
    while(_T--) {
        solve();
    }
}