import std.stdio, std.string, std.conv;
import std.range, std.algorithm, std.array, std.typecons, std.container;
import std.math, std.numeric, core.bitop;

enum inf3 = 1_001_001_001;
enum inf6 = 1_001_001_001_001_001_001L;
enum mod = 1_000_000_007L;


void main() {
    string n;
    scan(n);

    if (!n[1 .. $].all!"a == '3'") {
        writeln(-1);
    }
    else {
        writeln(n.count!"a == '3'");
    }
}



struct ModComb {
    int _N;
    long[] _fact, _factinv;
    long _mod;

    this(int n, long mod = 1_000_000_007L) {
        _N = n;
        _fact = new long[](_N + 1);
        _factinv = new long[](_N + 1);
        _mod = mod;

        _fact[0] = 1;
        foreach (i ; 1 .. _N + 1) {
            _fact[i] = (_fact[i-1] * i) % mod;
        }

        _factinv[_N] = _powmod(_fact[_N], mod - 2);
        foreach_reverse (i ; 0 .. _N) {
            _factinv[i] = (_factinv[i+1] * (i+1)) % mod;
        }
    }

    long c(int n, int k) {
        return f(n) * finv(n - k) % _mod * finv(k) % _mod;
    }

    long p(int n, int r) {
        return f(n) * finv(n - r) % _mod;
    }

    long f(int n) {
        return _fact[n];
    }

    long finv(int n) {
        return _factinv[n];
    }

    long _powmod(long x, long y) {
        return y > 0 ? _powmod(x, y>>1)^^2 % _mod * x^^(y & 1) % _mod : 1;
    }
}




void yes(bool b) {writeln(b ? "Yes" : "No");}
void YES(bool b) {writeln(b ? "YES" : "NO");}
T[] readArr(T)() {return readln.split.to!(T[]);}

void scan(T...)(ref T args) {
    import std.stdio : readln;
    import std.algorithm : splitter;
    import std.conv : to;
    import std.range.primitives;

    auto line = readln().splitter();
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}

void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}