/*
"An anomaly, I'm Muhammad Ali
  Cause I know one day I'm gonna be the"
                - Greatest, Eminem
*/
#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")
#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long int ll;
#define ff first
#define Shazam ios_base::sync_with_stdio(false);   cin.tie(NULL); cout.tie(NULL);
#define ss second
#define all(c) c.begin(),c.end()
#define endl "\n"
#define test() int t; cin>>t; while(t--)
#define fl(i,a,b) for(int i = a ; i <b ;i++)
#define get(a) fl(i,0,a.size())  cin>>a[i];
#define pra(a) fl(i,0,a.size()) cout<<a[i]<<" ";	cout<<endl;
#define pr(a,n) fl(i,0,n) cout<<a[i]<<" ";	cout<<endl;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
const ll INF = 2e18;
const int inf = 2e9;
const int mod1 = 1e9 + 7;



int main(){
    Shazam;
    long double a, b; cin >> a >> b;
    cout << fixed << setprecision(10) << a * b / 100.0 << endl;
    return 0;
}
//#define _GLIBCXX_DEBUG
//#include "atcoder/all"
//using namespace atcoder;
#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
#define Dump(x)                             \
    if (dbg) {                              \
        cerr << #x << " = " << (x) << endl; \
    }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) (((n) >> (k)) & 1) /*nのk bit目*/
namespace mydef {
const int INF = 1ll << 60;
const int MOD = 1e9 + 7;
template <class T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return 1;
    } else
        return 0;
}
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    } else
        return 0;
}
void Yes(bool flag = true) {
    if (flag)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
}
void No(bool flag = true) {
    Yes(!flag);
}
void YES(bool flag = true) {
    if (flag)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
}
void NO(bool flag = true) {
    YES(!flag);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T& val) {
    std::fill((T*)array, (T*)(array + N), val);
}
bool dbg = true;
}  // namespace mydef
using namespace mydef;
#define pb push_back
//#define mp make_pair
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vp vector<pair<int, int>>
#define vvp vector<vector<pair<int, int>>>
#define pi pair<int, int>
//#define P pair<int, int>
//#define V vector<int>
//#define S set<int>
#define asn ans

string S;

void solve() {
}

signed main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    cin >> S;
    int cnt[3] = {};
    for (auto& c : S)
        cnt[(c - '0') % 3]++;

    int SUM = cnt[1] + cnt[2] * 2;
    int ans = 0;
    if (SUM % 3 == 0) {
        ans = 0;
    } else if (SUM % 3 == 1) {
        if (cnt[1])
            ans = 1;
        else if (cnt[2] >= 2)
            ans = 2;
        else
            ans = -1;
    } else {
        if (cnt[2])
            ans = 1;
        else if (cnt[1] >= 2)
            ans = 2;
        else
            ans = -1;
    }
    if (ans == cnt[1] + cnt[2] + cnt[0])
        ans = -1;
    cout << ans << endl;

    solve();
    return 0;
}
