#include<bits/stdc++.h>
using namespace std;
//
typedef long double ld;
typedef long long int ll;
//
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
//
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<char> vc;
typedef vector<pii> vii;
typedef vector<pll> vll;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
#define prq priority_queue<ll>;
#define vbs(xx,x) binary_search(all(xx),x)
#define vlb(xx,x) lower_bound(all(xx),x)
#define vub(xx,x) upper_bound(all(xx),x)
//
ll MOD=998244353;
ll M=1e9+7;
#define PI 3.1415926535897932384626433832795
#define llMAX 1000000000000000008
#define llMIN -1000000000000000008
//
#define forx(i,j,n) for(long long int i=j;i<n;i++)
#define fory(i,j,n) for(long long int i=j;i>=n;i--)
#define all(x) x.begin(),x.end()
#define pb push_back
#define mp make_pair
#define fs first
#define sn second
#define mem(x,y) memset(x,y,sizeof(x))
//
#define nl "\n"
#define flush fflush(stdout)
clock_t tim;
void showtime(){ tim=clock()-tim; cout<<" ===> "<<(ld)tim/CLOCKS_PER_SEC<<" seconds\n"; }
//
ll mul(ll mul_1,ll mul_2){ ll mul_t=((mul_1%MOD)*(mul_2%MOD)+MOD)%MOD; return mul_t; }
ll mul3(ll mul_1,ll mul_2,ll mul_3){ ll mul_t=mul(mul(mul_1,mul_2),mul_3)%MOD; return mul_t; }
ll add(ll add_1,ll add_2){ ll add_t=((add_1%MOD)+(add_2%MOD)+MOD+MOD)%MOD; return add_t; }
ll sub(ll sub_1,ll sub_2){ ll sub_r=1e15; ll sub_t=(((sub_1+sub_r)%MOD)-((sub_2+sub_r)%MOD)+sub_r)%MOD; return sub_t; }
ll pwm(ll x,ll y,ll p=M){ ll res=1; x=x%p; while(y>0){ if(y&1) res=(res*x)%p; y=y/2; x=(x*x)%p; } return res; } 
ll pw(ll x,ll y){ ll res=1; while(y>0){ if(y&1) res=(res*x); y=y/2; x=(x*x); } return res; } 
ll modinv(ll n){ return pwm(n, M-2, M); }
ll gcd(ll num1,ll num2){ return (num2?gcd(num2,num1%num2):num1); }
ll lcm(ll num1,ll num2){ return 1LL*((num1*num2)/__gcd(num1,num2)); }
ll myceil(ll x,ll y){ return (x+y-1)/y;}
ll my_log(ll n,ll b){ll i = 1;ll ans = 0;while (1){if (i > n){ans--;break;}if (i == n)break;i *= b;ans++;}return ans;}
//
// ll countbit(ll num){ return 1LL*(__builtin_popcountll(num)); }
// ll setbit(ll num, ll kk){ return 1LL*(num|(1LL<<kk)); }
// ll unsetbit(ll num, ll kk){ return 1LL*(num&~(1LL<<kk)); }
// ll invertbit(ll num, ll kk){ return 1LL*(num^(1LL<<kk)); }
// bool kthbit(ll num, ll kk){ return num&(1LL<<kk); }
// ll zerotrail(ll num){ return 1LL*(__builtin_ctzll(num)); }
// ll zerobegin(ll num){ return 1LL*(__builtin_clzll(num)); }
// //
// ll prime[1000005]; 
// ll maxn=1e9+7;
// void sieve(){ forx(i,0,1000005) prime[i]=i; for(ll p=2; 1LL*p*p<maxn; p++){ if(prime[p]==p) { for(ll i=1LL*p*p; i<1000005; i+=p) if(prime[i]==i) prime[i]=p; } } return; } 
// bool isPrime(ll pri){if(pri==1||pri==0) return 0;if(prime[pri]==pri) return 1;return 0;}
// bool IsPrime(ll number){if (((!(number & 1)) && number != 2) || (number < 2) || (number % 3 == 0 && number != 3)) return false;for (ll k = 1; 36 * k * k - 12 * k < number; ++k) if ((number % (6 * k + 1) == 0) || (number % (6 * k - 1) == 0)) return false;return true;}
// vl alldiv(ll num){vl prDiv; for(ll i=1; 1LL*i*i<=num; i++){ if(num%i==0){ prDiv.pb(i); if(i!=(num/i)) prDiv.pb(num/i); } }sort(all(prDiv)); return prDiv;}
// vl prdiv(ll num){vl prDiv; while(num!=1){ prDiv.pb(prime[num]); ll prtemp=prime[num];  num/=prtemp; }return prDiv;}
// //
// bool ispalin(string d){ll n=d.length();for(ll i=0;i<n/2;i++){if(d[i]!=d[n-i-1]) return 0;}return 1;}
// //
// const int MAX=2*100005;
//
// bool vis[MAX];
// vvi adj(MAX);
// ll dep[MAX];
// ll ht[MAX];
// vl diff;
// void dfs(int s,int p){
//     vis[s]=true;
//     if(p!=-1) ht[s]=ht[p]+1;
//     for(auto i:adj[s]){
//         if(!vis[i]) {
//             dfs(i,s);
//             dep[s]+=1+dep[i];
//         }
//     }
//     diff.pb(dep[s]-ht[s]);
// }
// ll sos(ll a,ll b,ll c){
//     return (a-b)*(a-b)+(b-c)*(b-c)+(c-a)*(c-a);
// }

void solve(){
   ll n,j=0,k,m,f=0,p,q;
   string s,t;
   cin>>s>>t;
   n=s.length();
   k=t.length();
   forx(i,0,n){
       if(s[i]!=t[i]) f++;
   }
   cout<<f<<"\n";
   
    
    
    
}

int main(){

ios_base::sync_with_stdio(false);
cin.tie(NULL);

ll x=1;
forx(u,0,x){
   //cout<<"Case #"<<h+1<<":"<<" ";
   solve();
}
return 0;
}

Measured memory_bytes: 3764