求助qwq 求组合数的乘法逆元时出现了问题

ll fac(ll x){
    ll mul = 1;
    for(int i = 2; i <= x; i++) mul = (mul * i % mod) % mod;
    return mul;
}

ll C(ll n, ll m){
    ll j1 = fac(n);
    ll j2 = inv(fac(m));
    ll j3 = inv(fac(n - m));
    return (j1 * j2 * j3) % mod;
}

ll fac(ll x){
    ll mul = 1;
    for(int i = 2; i <= x; i++) mul = (mul * i) % mod;
    return mul;
}

ll C(ll n, ll m){
    ll j1 = fac(n);
    ll j2 = fac(m);
    ll j3 = fac(n - m);
    j2 = (j2 * j3) % mod;
    return j1 * inv(j2) % mod;
}