View Compilation Error

0_0_30880595_11876.cpp: In function 'll solve()':
0_0_30880595_11876.cpp:30:27: error: invalid initialization of reference of type 'll& {aka long long int&}' from expression of type 'int'
         d = gcd(M,m[i],x,y);
                           ^
0_0_30880595_11876.cpp:6:4: note: in passing argument 3 of 'll gcd(ll, ll, ll&, ll&)'
 ll gcd(ll a,ll b,ll &x,ll &y)
    ^