#include<bits/stdc++.h>
using namespace std;
#define fs first
#define sc second
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define ALL(A) A.begin(),A.end()
#define RALL(A) A.rbegin(),A.rend()
typedef long long LL;
typedef pair<LL,LL> P;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<typename T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
const LL mod=1000000007;
const LL LINF=1LL<<62;
const int INF=1<<30;
int dx[]={1,0,-1,0,1,-1,1,-1};
int dy[]={0,1,0,-1,1,-1,-1,1};
 

int main(){
    int a,b;cin >> a >> b;
    auto f = [&](int k){
        int n = a * k + b * k;
        vector<int> p(n + 1, 1);
        p[0] = 0;
        for (int i = 0; i * a <= n; i++) {
            for (int j = 0; i * a + j * b <= n; j++) {
                p[a * i + b * j] = 0;
            }
        }
        int ret = 0;
        for (int i = 0; i <= a * k + b * k; i++) {
            ret += p[i];
        }
        return ret;
    };
    int A = f(100) , B = f(200);
    if(A == B) cout << A << endl;
    else cout << -1 << endl;
    return 0;
}