谁能帮我看一下这道题我的代码的错误：

https://www.luogu.com.cn/problem/U204727

错误代码：

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,m,q,cnt[1000005][26],a,b;
string s;
char ch;
ll mod(ll a){
    ll a0 = (a % n == 0) ? n : a % n;
    return a0;
}
ll pre(ll a,ll b,ll c){
    ll x = cnt[mod(b)][c] - cnt[mod(a) - 1][c] + (b - a + 1) / n * cnt[n][c];
    return x;
}
int main(){
    cin>>n>>m>>q;
    cin>>s;
    for(ll i = 1;i <= n;i++){
        for(ll j = 0;j < 26;j++){
            cnt[i][j] = cnt[i - 1][j];
        }
        cnt[i][s[i - 1] - 'a']++;
    }
    for(ll i = 1;i <= q;i++){
        cin>>a>>b;
        cin>>ch;
        ll x;
        if(mod(b) < mod(a)){
            x = cnt[mod(b)][ch];
            b -= mod(b);
        }
        x += pre(a,b,ch - 'A');
        cout<<x<<endl;
    }
    return 0;
}