#include <bits/stdc++.h>
using namespace std;
const long long N = 2e5 + 7;
const string alpha = "abcdefghijklmnopqrstuvwxyz";
long long power(long long x, long long y) {
  long long res = 1;
  x = x;
  while (y > 0) {
    if (y & 1) res = (res * x);
    y = y >> 1;
    x = (x * x);
  }
  return res;
}
template <typename T>
T gcd(T a, T b) {
  if (a == 0) return b;
  return gcd(b % a, a);
}
template <typename T>
T powm(T a, T b, long long m) {
  T cnt = 1;
  while (b > 0) {
    if (b % 2 == 1) cnt = (cnt * a) % m;
    b /= 2;
    a = (a * a) % m;
  }
  return cnt % m;
}
long long ncr(long long n, long long r) {
  long long res = 1;
  if (r > n) return 0;
  if (r > n - r) r = n - r;
  for (long long i = 0; i < r; i++) {
    res *= (n - i);
    res /= (i + 1);
  }
  return res;
}
long long sqr(long long x) { return x * x; }
void solve() {
  string s;
  cin >> s;
  int n = (long long)s.size(), one = 0, two = 0;
  if (n % 2) {
    cout << "-1";
    return;
  }
  for (long long i = 0; i < n; ++i) {
    if (s[i] == 'L') one++;
    if (s[i] == 'R') one--;
    if (s[i] == 'U') two++;
    if (s[i] == 'D') two--;
  }
  cout << (abs(one) + abs(two)) / 2;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int tc;
  tc = 1;
  while (tc--) solve();
  return 0;
}
