Bear And Steady Gene - readable code

BearAndSteadyGene_Readable.cs

using System;
using System.Collections.Generic;
using System.IO;
class Solution {
    static void Main(String[] args) {
        int N = Int32.Parse(Console.ReadLine());
        int A = 0;
        int C = 0;
        int G = 0;
        int T = 0;
        string line = Console.ReadLine();
        for(int i=0; i<N; i++) {
            switch(line[i]) {
                case 'A': A++; break;
                case 'C': C++; break;
                case 'G': G++; break;
                case 'T': T++; break;
            }
        }
        A -= N/4; C -= N/4; G-= N/4; T -= N/4;
        if(A == 0 && C == 0 && G == 0 && T == 0) {
            Console.WriteLine("0");
        } else if(A+C+G+T == 1) {
            Console.WriteLine("1");
        } else {
            int min = N;
            int best = Math.Max(0,A) + Math.Max(0,C) + Math.Max(0,G) + Math.Max(0,T);
            int start = 0;
            int end = 0;
            switch(line[0]) {
                case 'A': A--; break;
                case 'C': C--; break;
                case 'G': G--; break;
                case 'T': T--; break;
            }            
            while(min != best && start<N && end<N) {
                if(A <= 0 && C <=0 && G <= 0 && T <= 0) {
                    if(end-start+1 < min)
                        min = end-start+1;
                    switch(line[start]) {
                        case 'A': A++; break;
                        case 'C': C++; break;
                        case 'G': G++; break;
                        case 'T': T++; break;                        
                    }
                    start++;
                } else {
                    end++;
                    if(end != N) {
                        switch(line[end]) {
                            case 'A': A--; break;
                            case 'C': C--; break;
                            case 'G': G--; break;
                            case 'T': T--; break;                                                
                        }
                    }
                }
            }
            Console.WriteLine(min);
        }
    }
}