Submission #18

#include<bits/stdc++.h>
using namespace std;
#ifndef BADGNU
#pragma GCC target("sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#endif
#pragma GCC optimize("Ofast,unroll-loops,fast-math,O3")
#define ll long long
// #define int ll
#define ld long double
#define y1 cheza
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int N=1e5+100;
const int M=5001;
const int B=447;
const int mod=998244353;
const ll INF=1e18;
const int dx[]={1,-1,0,0};
const int dy[]={0,0,1,-1};
const double eps=1e-6;
string a;     
void test(){
    char b;
    while(cin>>b){
        a.push_back(b);
    }
    int ans=0;
    for(int i=0;i<a.size()>>1;i++){
        if(a[i]!=a[i+(a.size()>>1)]){
            ans++;
        }
    }
    cout<<ans<<'\n';
}




/*

*/
signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    // cout.tie(nullptr);
    int t2=1;
    // cin>>t2;
    for(int i=1;i<=t2;i++){
        test();
    }
}