Afin1

#include <bits/stdc++.h>

using namespace std;
ifstream fin("afin1.in");
ofstream fout("afin1.out");
int a, b, expr[27];
string mess;
int modInverse(int a, int b)
{
	int b0 = b, t, q;
	int x0 = 0, x1 = 1;
	if (b == 1) return 1;
	while (a > 1)
    {
		q = a / b;
		t = b, b = a % b, a = t;
		t = x0, x0 = x1 - q * x0, x1 = t;
	}
	if (x1 < 0) x1 += b0;
	return x1;
}
int main()
{
    fin>>a>>b;
    fin>>mess;
    for(int i=0; i<26; i++)
        expr[i]=(a*i+b)%26;
    int ok=0;
    for(int i=0; i<25 && !ok; ++i)
        for(int j=i+1; j<26 && !ok; ++j)
            if(expr[i]==expr[j])
                ok=1;
    if(ok)
    {
        fout<<-1;
        return 0;
    }
    for(int i=0; mess[i]; ++i)
        fout << (char)(modInverse(a, 26) * (26 + mess[i] - 'a' - b) % 26 + 'a');
    return 0;
}