#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <list>
#include <bitset>
#include <numeric>
#include <unordered_map>
#include <unordered_set>
 
using namespace std;
 
#define R 1000000007
#define M 998244353

int mx = 0, mn = INT32_MAX;

struct dsu
{
    vector<int> rank, parent;
    dsu(int n)
    {
        rank.assign(n, 0);
        parent.resize(n);
        for(int i = 0; i < n; i++)
            parent[i] = i;
    }
    int find_set(int i)
    {
        if(i == parent[i])
            return i;
        return parent[i] = find_set(parent[i]);
    }
    bool is_same_set(int i, int j)
    {
        if(find_set(i) == find_set(j))
            return true;
        return false;
    }
    void union_set(int i, int j)
    {
        if(!is_same_set(i, j))
        {
            int u = find_set(i), v = find_set(j);
            if(rank[u] == rank[v])
            {
                parent[v] = u;
                rank[u] += 1;
            }
            else if(rank[u] > rank[v])
                parent[v] = u;
            else 
                parent[u] = v;
        }
    }

};

struct graph
{
    int v, time, count;
    vector<pair<int, int>>* adj;
    vector<bool> visited, in_stack;
    stack<int> s;
    vector<int> color, cc, d, f, l, finish_time, indegree, sccs, topo, outdegree;
    graph(int n)
    {
        v = n;
        adj = new vector<pair<int, int>>[n];
        visited.assign(n, false);
        in_stack.assign(n, false);
        color.assign(n, 0);
        cc.assign(n, -1);
        d.assign(n, -1);
        f.assign(n, -1);
        indegree.assign(n, 0);
        outdegree.assign(n, 0);
        time = count = 0;
        finish_time.assign(2 * n, -1);
        l.assign(n, 0);
    }
    void add_edge(int u, int v, int w)
    {
        adj[u].push_back(make_pair(v, w));
        //adj[v].push_back(make_pair(u, w));
    }

    void dfs()
    {
        color.assign(v, 0);
        cc.assign(v, -1);
        time = count = 0;
        finish_time.assign(2 * v, -1);
        visited.assign(v, false);
        for(int i = 0; i < v; i++)
        {
            if(color[i] == 0)
            {
                dfs(i);
                count++;
            }
        }
        for(int i = 0; i < v; i++)
            finish_time[f[i]] = i;
    }
    void dfs(int i)
    {
        color[i] = 1;
        cc[i] = count;
        d[i] = time;
        time++;
        for(auto x : adj[i])
            if(color[x.first] == 0)
                dfs(x.first);
        color[i] = 2;
        f[i] = time;
        time++;
    }

    void scc()
    {
        graph g_t(v);
        for(int i = 0; i < v; i++)
            for(auto x : adj[i])
                g_t.add_edge(x.first, i, x.second);
        dfs();
        for(int i = 2 * v - 1; i >= 0; i--)
        {
            if(finish_time[i] != -1 && g_t.color[finish_time[i]] == 0)
            {
                g_t.dfs(finish_time[i]);
                g_t.count++;
            }
        }
        sccs = g_t.cc;
        count = g_t.count;
    }

    void topological_sort()
    {
        for(int i = 0; i < v; i++)
            if(adj[i].size())
                outdegree[i] = adj[i].size();
        for(int i = 0; i < v; i++)
            for(auto x : adj[i])
                indegree[x.first]++;
        vector<int> zero;
        for(int i = 0; i < v; i++)
            if(!indegree[i])
                zero.push_back(i);
        
        while(!zero.empty())
        {
            int v = zero.back();
            topo.push_back(v);
            zero.pop_back();
            for(auto x : adj[v])
            {
                indegree[x.first]--;
                if(!indegree[x.first])
                    zero.push_back(x.first);
            }
        }
    }

    void tarjan()
    {
        for(int i = 0; i < v; i++)
            if(!color[i])
                tarjan(i);
    }
    void tarjan(int i)
    {
        color[i] = 1;
        d[i] = time;
        time++;
        l[i] = d[i];
        s.push(i);
        in_stack[i] = true;
        for(auto x : adj[i])
        {
            if(!color[x.first])
            {
                tarjan(x.first);
                l[i] = min(l[i], l[x.first]);
            }
            else if(in_stack[x.first])
            {
                l[i] = min(l[i], d[x.first]);
            }
        }
        
        color[i] = 2;
        f[i] = time;
        time++;
        if(d[i] == l[i])
        {
            while(s.top() != i)
                cout << s.top() << ' ', in_stack[s.top()] = false, s.pop();
            cout << s.top() << '\n', in_stack[s.top()] = false, s.pop();
        }
    }
};

struct kmp
{
    vector<int> lps;
    string p, t;
    kmp(string& p, string& t)
    {
        this -> p = p;
        this -> t = t;
        //PREPROCESSING
        lps.assign(p.size(), 0);
        lps[0] = 0;
        int len = 0, i = 1, j;
        while(i < p.size())
        {
            if(p[i] == p[len])
                lps[i++] = ++len;
            else if(len)
                len = lps[len-1];
            else 
                lps[i++] = 0;
        }
        //STRING MATCHING
        i = j = 0;
        while(i < t.size())
        {
            if(p[j] == t[i])
                j++, i++;
            
            if(j == p.size())
                j = lps[j-1];
            else if(i < t.size() && p[j] != t[i])
            {
                if(j)
                    j = lps[j-1];
                else 
                    i++;
            }
        }

        
    }
};

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int a, b;
    cin >> a >> b;
    int min_b = 10 * b, max_b = 10 * b + 9;
    int min_a = (25 * a) / 2, max_a;
    if(a % 2 == 1)
        min_a = ((25 * a) / 2) + 1;
    if(a % 2 == 1) 
        max_a = ((25 * (a + 1)) / 2) - 1;
    else
        max_a = ((25 * (a + 1)) / 2);
    if(max_a < min_b || max_b < min_a)
    {
        cout << "-1\n";
    }
    else 
    {
        if(min_a > min_b)
            cout << min_a << '\n';
        else    
            cout << min_b << '\n';
    }
    return 0;
}

Measured memory_bytes: 256