#include<bits/stdc++.h>
using namespace std;
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define endl "\n";
long long M = 1e9+7;
long long power(long long a, long long p)
{
    if(p==0) return 1;
    long long ans= power(a,p/2);
    ans =(ans * ans) % M;
    if(p%2) ans = (ans*a) % M;
    return ans;
}

long long SieveOfEratosthenes(long long n, long long a)
{
    bool prime[n+1];
    memset(prime, true, sizeof(prime));
    for (long long p=2; p*p<=n; p++)
    {
        if (prime[p] == true)
        {
            for (long long i=p*p; i<=n; i += p)
                prime[i] = false;
        }
    }
    for (long long p=2; p<=n; p++)
       if (prime[p])
       {
           if(a%p==0)
           {
               return (a-p);
           }
       }
}
long long nCr(int n, int r)
{
    if(r > n - r) r = n - r; // because C(n, r) == C(n, n - r)
    long long ans = 1;
    int i;
    for(i = 1; i <= r; i++) {
        ans *= n - r + i;
        ans /= i;
    }
    return ans;
}

//int vis[1001][1001];
//int x[]={1,0};
//int y[]={0,-1};
 /*int dfs_visit(long long r, long long c)
{
    int flag=0;
    vis[r][c]=1;
    for(int i=0; i<2; i++)
    {

        int p=r+x[i];
        int q=c+y[i];
        if(p==(a-1) && q==(b-1))
        {
            flag=1;
            break;
        }
        if(p>=0 && p<a && q>=0 && q<b && vis[p][q]==0 && v[p][q]!='#')
        {
           // cout<<p<<" "<<q<<endl;

            vis[p][q]=1;
            dfs_visit(p,q);

        }
    }
    if(flag==1)
    {
        return 2;
    }
    else
    {
        return 3;
    }

}
*/

long long fun(long long abc)
{
    long long coo;
    while(abc>0)
    {
        if(abc%2!=0)
        {
            coo++;
        }
        abc/=2;
    }
    return coo;
}
#define mx 100005
int arr[mx];
int tree[mx * 4];
void init(int node, int b, int e)
{
    if (b == e) {
        tree[node] = arr[b];
        return;
    }
    int Left = node * 2;
    int Right = node * 2 + 1;
    int mid = (b + e) / 2;
    init(Left, b, mid);
    init(Right, mid + 1, e);
    tree[node] = tree[Left] + tree[Right];
}
int query(int node, int b, int e, int i, int j)
{
    if (i > e || j < b)
        return 0; //বাইরে চলে গিয়েছে
    if (b >= i && e <= j)
        return tree[node]; //রিলেভেন্ট সেগমেন্ট
    int Left = node * 2; //আরো ভাঙতে হবে
    int Right = node * 2 + 1;
    int mid = (b + e) / 2;
    int p1 = query(Left, b, mid, i, j);
    int p2 = query(Right, mid + 1, e, i, j);
    return p1 + p2; //বাম এবং ডান পাশের যোগফল
}
void update(int node, int b, int e, int i, int newvalue)
{
    if (i > e || i < b)
        return; //বাইরে চলে গিয়েছে
    if (b >= i && e <= i) { //রিলেভেন্ট সেগমেন্ট
        tree[node]=newvalue;
        return;
    }
    int Left = node * 2; //আরো ভাঙতে হবে
    int Right = node * 2 + 1;
    int mid = (b + e) / 2;
    update(Left, b, mid, i, newvalue);
    update(Right, mid + 1, e, i, newvalue);
    tree[node] = tree[Left] + tree[Right];
}

int main()
{
    IOS;
    long long a,b,c,d,e,h,l,n,t,f,m,x,y,z,f1=0,flag=0,flag1=0,co=0,co1=0,co2=0,sum=0,sum1=0,ma=0,ma1=0,mi=1000000000000000001;
    long long g,co3=0,co4=0,co5=0,co6=0,co7=0,co8=0,mul=1,sum2=0,sum3=0,mu=1,mu1=1;
    long long a1,b1,a2,b2,a3,b3,a4,b4,a5,b5,b6;
    double pi=2 * acos (0.0);
    string str,str1,str2,str3,str4,str5,str6;
    char ch,ch1;
    //int x[]={1,1,1,0,0,-1,-1,-1};
    //int y[]={0,1,-1,1,-1,1,-1,0};
    //int x[]={1,0,0,-1};
    //int y[]={0,1,-1,0};
    cin>>str>>str1;
    for(int i=0; i<str.size(); i++)
    {
        if(str[i]!=str1[i])
        {
            co++;
        }
    }
    cout<<co<<endl;
    return 0;
}


Measured memory_bytes: 3784