Find the minimum time

Geek wants to scan N documents using two scanners. If S1 and S2 are the time taken by the scanner 1 and scanner 2 to scan a single document, find the minimum time required to scan all the N documents.

• Time : O(log(min(t1, t2) * n))
• Space : O(1)

class Solution{
public:
    int minTime(int t1, int t2, int N){
        int l = 0, r = min(t1, t2) * N, res = INT_MAX;
        while(l <= r) {
            int m = l + (r - l) / 2;
            int scan = m / t1 + m / t2;
            
            if(scan >= N) res = min(res, m);
            if(scan >= N) r = m - 1;
            else l = m + 1;
        }
        return res;
    }