Thread.CurrentThread.CurrentCulture = CultureInfo.InvariantCulture;

            var tokens = Console.ReadLine().Trim().
                Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries);

            var a = int.Parse(tokens[0]);
            var b = int.Parse(tokens[1]);
            var c = int.Parse(tokens[2]);
            var d = int.Parse(tokens[3]);

            var min = a + (c - a) / (b + d) * b;
            var max = c - (c - a) / (b + d) * d;

            min = Math.Min(min + b, Math.Max(min, max));
            max = Math.Max(max - d, min);

            Console.WriteLine(max);

Corrected, see !!! sign

            Thread.CurrentThread.CurrentCulture = CultureInfo.InvariantCulture;

            var tokens = Console.ReadLine().Trim().
                Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries);

            var a = int.Parse(tokens[0]);
            var b = int.Parse(tokens[1]);
            var c = Math.Max(int.Parse(tokens[2]), a); // !!!!
            var d = int.Parse(tokens[3]);

            var min = a + (c - a) / (b + d) * b;
            var max = c - (c - a) / (b + d) * d;

            min = Math.Min(min + b, max);
            max = Math.Max(max - d, min);

            Console.WriteLine(max);
        }

This is strange: "The driver would not ask a sum that is less than that offered by Petr."

#include<bits/stdc++.h>

using namespace std;

int gcd(int a,int b){
    if(b==0)return a;
    return gcd(b,a%b);
}


int main()
{
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    int carry=(c-a)%(b+d);
    int res=(c-a)/(b+d);
    if(carry==0){
        cout<<a+res*b<<'\n';
    }
    else if(carry>=b){
        cout<<a+(res+1)*b<<'\n';
    }
    else if(carry<b){
        cout<<c-res*d<<'\n';
    }
}



why wrong ans in test #6?