/*
AUTHOR : Chandan Agrawal
College : Poornima College of Engg. jaipur, Raj
Mail : chandanagrawal23@gmail.com
*/

#include<bits/stdc++.h>
#include<stdio.h>
using namespace std;

#define fastio ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define MAX 10000050

#define ll long long
#define ld long double
#define lli long long int

#define pb emplace_back
#define INF 1000000000
#define mod 1000000007

// trignometric function always give value in Radians only
#define PI acos(-1) //3.1415926535897932384626433832795028
#define dsin(degree) sin(degree*(PI/180.0))
#define dcos(degree) cos(degree*(PI/180.0))
#define dtan(degree) tan(degree*(PI/180.0))

#define rsin(radian) sin(radian)
#define rcos(radian) cos(radian)
#define rtan(radian) tan(radian)

#define loop(i,n) for (lli i = 0; i < n; i++)
#define loopitr(xt,vec) for (auto xt : vec)
#define FOR(i,a,b) for (lli i = a; i < b; i+=1)
#define loop_rev(i,n) for (lli i = n-1; i >= 0; i--)
#define FOR_REV(i,a,b) for (lli i = a; i >= b; i--)
#define itr :: iterator it
#define WL(t) while(t --)

#define all(v) v.begin(),v.end()
#define sz(x) int(x.size())
#define F first
#define S second

#define mii map<lli,lli>
#define vi vector<lli>
#define seti set<lli>
#define pii pair<lli,lli>

#define gcd(a,b) __gcd((a),(b))
#define lcm(a,b) (a/gcd(a,b))*b
#define abs(x) ((x < 0)?-(x):x)

template <typename T>
void print(T x){cout<<x<<endl;}
template <typename T1, typename T2>
void print2(T1 x,T2 y){cout<<x<<" "<<y<<endl;}
template <typename T1, typename T2,typename T3>
void print3(T1 x, T2 y,T3 z){cout<<x<<" "<<y<<" "<<z<<endl;}

#define scanarr(a,n) for(lli i=0;i<n;i++)    cin>>a[i];
#define scanvector(a,n) for(lli i=0;i<n;i++){ lli x ; cin>>x; a.pb(x);}

#define printarr(a,n) for(lli i=0;i<n;i++)   cout<<a[i]<<" "; cout<<endl;
#define printvector(vec) for(auto xt : vec) cout<<xt<<" ";    cout<<"\n";
#define printset(st) for(auto xt : st) cout<<xt<<" ";    cout<<"\n";

#define FD(N) fixed<<setprecision(N)

#define endl '\n'

#define deb(x) cout<<#x<<" "<<x<<endl;

// chandan1,2
void chandan1(){int y=1;return;}
void chandan2(){
        loop(i,10){
        lli x=1;
    }
    return(chandan1());
}

lli spf[MAX+1];

void sieve2(){ //smallest prime factor of N.

    loop(i,MAX+1) spf[i]=i;
    for(lli i=4;i<=MAX;i+=2) spf[i]=2;

    for(lli i=3; i*i<=MAX; i+=2){
        if (spf[i] == i){
            for (int j=i*i; j<=MAX; j+=i)
                if (spf[j]==j) //marking spf[j] if it is not previously marked
                    spf[j] = i;
        }
    }
}

lli tfactor[MAX+1];
lli sumfactor[MAX+1];
lli dp[MAX+1];
void sieve4(){ // totalfactor and sum_of_all_factors
    // n = (a^p)*(b^q)*(c^r)....
    // totalfactors = (p+1)*(q+1)*(r+1)...
    // sumoffactors =  [(a^(p+1)-1)/(a-1))]*[(b^(q+1)-1)/(b-1))]*[(c^(r+1)-1)/(c-1))]....
    sieve2();
    tfactor[1] = sumfactor[1] = dp[1] = 1;
    for(lli i=2;i<=MAX;i++){
        lli mspf = spf[i];
        lli prim = mspf;
        lli temp = i;
        lli cnt=0;
        while(temp%mspf==0){
            temp/=mspf;
            cnt+=1;
            prim = prim*mspf;
        }
        tfactor[i] = (cnt+1) * tfactor[temp];
        sumfactor[i] = (prim -1)/(mspf-1) * sumfactor[temp];
        dp[i] = dp[i-1]+i*tfactor[i];
     }
}

int main(){
fastio
lli t=1;
//cin>>t;
//sieve4();
while(t--) {
    lli n;
    string a,b;
    cin>>a>>b;
    lli cnt=0;
    loop(i,sz(a)){
        if(a[i]!=b[i])
            cnt++;
    }
    print(cnt);
  }
return 0;
}


Measured memory_bytes: 3800