#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <climits>
#include <cstring>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <vector>
#include <list>
#define rep(i,m,n) for(i=m;i<=n;i++)
#define rsp(it,s) for(set<int>::iterator it=s.begin();it!=s.end();it++)
const int inf_int = 2e9;
const long long inf_ll = 2e18;
#define inf_add 0x3f3f3f3f
#define mod 1000000007
#define vi vector<int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define pi acos(-1.0)
#define pii pair<int,int>
#define Lson L, mid, rt<<1
#define Rson mid+1, R, rt<<1|1
const int maxn=5e2+10;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
inline int read(){int ra,fh;char rx;rx=getchar(),ra=0,fh=1;
while((rx<'0'||rx>'9')&&rx!='-')rx=getchar();if(rx=='-')
fh=-1,rx=getchar();while(rx>='0'&&rx<='9')ra*=10,ra+=rx-48,
rx=getchar();return ra*fh;}
//#pragma comment(linker, "/STACK:102400000,102400000")
ll gcd(ll p,ll q){return q==0?p:gcd(q,p%q);}
ll qpow(ll p,ll q){ll f=1;while(q){if(q&1)f=f*p;p=p*p;q>>=1;}return f;}
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
ll ct1,ct2,ct3,ct4,re;
string s;
int main(int argc, char** argv)
{
cin >> s;
if(s.length()%2)
{
cout << "-1" << endl;
return 0;
}
for(int i=0;i<s.length();i++)
{
if(s[i]=='U')
ct1++;
else if(s[i]=='D')
ct2++;
else if(s[i]=='R')
ct3++;
else if(s[i]=='L')
ct4++;
}
ll t1 = abs(ct1-ct2);
ll t2 = abs(ct3-ct4);
if(t1>t2) swap(t1,t2);
re += t1;
re += (t2-t1)/2;
cout << re << endl;
return 0;
}