#include <bits/stdc++.h>
using namespace std;
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1};
#define endl "\n"
using ull=unsigned long long;
using ll=long long;
using pii=pair<int,int>;
const int mod=1e9+7;
#define OVL(x,s) for(auto y:x) cout<<y<<s; cout<<"\n";
template <typename T> istream& operator>>(istream& is, vector<T> &a) {
copy_n(istream_iterator<T>(is), a.size(), a.begin()); return is;}
#ifdef IOI
void dbg_out() { cout << endl; } template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cout << ' ' << H; dbg_out(T...); }
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__);
#else
#define dbg(...) 1337;
#endif
#define pb push_back
#define F first
#define S second
#define all(v) v.begin(),v.end()
const int mxn=1e5+100;
vector<vector<int>> freq1,freq2;
vector<int> eq;
int n;
map<char,int> mp;
vector<vector<vector<int>>> pref;
int sum(int w,int a,int b,vector<vector<int>> &pref){
if(a==0) return pref[b][w];
else return pref[b][w]-pref[a-1][w];
}
int sum(int l,int r,vector<int>& pref){
if(l==0) return pref[r];
return pref[r]-pref[l-1];
}
void init(string a,string b){
mp['A']=0;
mp['T']=1;
mp['C']=2;
n=a.length();
freq1.resize(n+1,vector<int>(3,0));
freq2.resize(n+1,vector<int>(3,0));
pref.resize(n+1,vector<vector<int>>(3,vector<int>(3,0)));
eq.resize(n+1,0);
for(int i=0;i<n;i++){
freq1[i][mp[a[i]]]++;
freq2[i][mp[b[i]]]++;
if(!i) continue;
for(int j=0;j<3;j++){
freq1[i][j]+=freq1[i-1][j];
freq2[i][j]+=freq2[i-1][j];
}
}
for(int i=0;i<n;i++){
eq[i]=(a[i]==b[i]);
if(i) eq[i]+=eq[i-1];
}
for(int i=0;i<n;i++){
pref[i][mp[a[i]]][mp[b[i]]]++;
if(!i) continue;
for(int j=0;j<3;j++){
for(int k=0;k<3;k++){
pref[i][j][k]+=pref[i-1][j][k];
}
}
}
}
int sum(int a,int b,int l,int r,vector<vector<vector<int>>> &pref){
if(l==0) return pref[r][a][b];
else return pref[r][a][b]-pref[l-1][a][b];
}
int get_distance(int x,int y){
bool ok=true;
for(int i=0;i<3;i++){
ok&=(sum(i,x,y,freq1)==sum(i,x,y,freq2));
}
if(!ok) return -1;
int rest=y-x+1;
int ans=0;
rest-=sum(x,y,eq);
map<int,int> mp;
for(int i=0;i<3;i++){
for(int j=i+1;j<3;j++){
int a=sum(i,j,x,y,pref)-mp[i];
int b=sum(j,i,x,y,pref)-mp[j];
int c=min(a,b);
if(c<=0) continue;
mp[i]+=c;
mp[j]+=c;
int k=2*c;
ans+=c;
rest-=2*c;
}
}
ans+=max(0,rest-1);
return ans;
}
#ifdef IOI
signed main(){
int n,q;
cin>>n>>q;
string a;
cin>>a;
string b;
cin>>b;
init(a,b);
while(q--){
int a,b;
cin>>a>>b;
int x=get_distance(a,b);
cout<<x<<endl;
}
}
#endif
