#include <iostream>
#include <stdlib.h>

using namespace std;

void xgcd(int *result, int a, int b)
{
    long aa[2]={1,0}, bb[2]={0,1}, q;
    while(1) {
        q = a / b; a = a % b;
        aa[0] = aa[0] - q*aa[1];  bb[0] = bb[0] - q*bb[1];
        if (a == 0) {
            result[0] = b; result[1] = aa[1]; result[2] = bb[1];
            return;
        };
        q = b / a; b = b % a;
        aa[1] = aa[1] - q*aa[0];  bb[1] = bb[1] - q*bb[0];
        if (b == 0) {
            result[0] = a; result[1] = aa[0]; result[2] = bb[0];
            return;
        };
    };
}

int main()
{
    int a, b, c[3];
    cin>>a>>b;
    if(b==0)
        cout<<"-1";
    else
    {xgcd(c,a,b);
    if(c[0]==1)
    {
        if(c[2]<0)
            c[2]+=a;
        cout<<c[2];
    }
    else
        cout<<"-1";}
}