//----AUTHOR:kkdrummer----/
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
//#include <boost/multiprecision/cpp_int.hpp> 
//using namespace boost::multiprecision; 
using namespace __gnu_pbds;
using namespace std;
typedef    long long                 ll;
typedef    long double               ld;
typedef    unordered_set<ll>         usll;
typedef    unordered_multiset<ll>    umsll;
typedef    multiset<ll>              msll;
typedef    set<ll>                   sll;
typedef    vector<ll>                vll;
typedef    pair<ll,ll>               pll;
typedef    vector<pll>               vpll;
typedef    priority_queue<ll>        pqll;
typedef    vector<int>               vi;
typedef    set<int>                  si;
typedef    multiset<int>             msi;
typedef    unordered_multiset<int>   umsi;
typedef    unordered_set<int>        usi;
typedef    pair<int,int>             pi;
typedef    vector<pi>                vpi;
typedef    priority_queue<int>       pqi;
typedef    tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>   ind_si;
typedef    tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>   ind_sll;
typedef    tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update>   ind_msi;
typedef    tree<ll,null_type,less_equal<ll>,rb_tree_tag,tree_order_statistics_node_update>   ind_msll;
#define    in          insert
#define    fi          first
#define    se          second
#define    pb          push_back
#define    mp          make_pair
#define    be          begin
#define    en          end
#define    itr         iterator
#define    io          ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define    mo          1000000007
#define    inf         9222372026854775807
#define    ninf        -inf
#define    ima         2047483647
#define    imi         -ima
#define    oncnt       __builtin_popcount
#define    zerobegin   __builtin_clz
#define    zeroend     __builtin_ctz
#define    parity      __builtin_parity
#define    all(x)      x.be(),x.en()
#define    eps         1e-9
#define    coutd       cout<<setprecision(12)<<fixed
#define    mems(dp,x)  memset(dp,x,sizeof(dp))
#define    fbo         find_by_order
#define    ook         order_of_key
#define    upb         upper_bound
#define    lowb        lower_bound 
#define    lte(v,x)    upb(all(v),x)-v.be()
#define    gte(v,x)    v.end()-lowb(all(v),x)
#define    gt(v,x)     v.en()-upb(all(v),x)
#define    lt(v,x)     lowb(all(v),x)-v.be()
const      ld PI=      3.1415926535897932384626433832792884197169399375105820974944;
inline ll modpow(ll x,ll n){if(n==0)return 1;if(x==0)return 0;if(n==1)return(x%mo);ll u=(modpow(x,n/2));u=(u*u)%mo;if(n%2!=0)u=(u*x%mo)%mo;return u;}
inline ll modinv(ll x){return modpow(x,mo-2);}
inline ll mmul(ll a,ll b){if(a>=mo)a=a%mo;if(b>=mo)b=b%mo;if(a*b>=mo)return(a*b)%mo;return(a*b);}
inline ll madd(ll a, ll b){if(a>=mo)a=a%mo;if(b>=mo)b=b%mo;if(a+b>=mo)return(a+b)%mo;return(a+b);}
inline ll msub(ll a, ll b){if(a>=mo)a=a%mo;if(b>=mo)b=b%mo;return(((a-b)%mo+mo)%mo);}
inline ll mdiv(ll a,ll bb){if(a>=mo)a=a%mo;ll b=modinv(bb);if(b>=mo)b=b%mo;if(a*b>=mo)return(a*b)%mo;return(a*b);}
inline ll gcd(ll a,ll b){return __gcd(a,b);}
inline ll lcm(ll a,ll b){return (a*b)/gcd(a,b);}
 
 



int main()
{             io 
int testcases=1;           //         cin>>testcases;
while(testcases--)
{




string a,b;
cin>>a>>b;

int c=0;
for(int i=0;i<a.length();i++)
{
	if(a[i]!=b[i])
	c++;
}

cout<<c;






























































 
 
}return 0;}

Measured memory_bytes: 3812