def min_Swaps(s1,s2) :  
    c0 = 0; c1 = 0;  
    for i in range(len(s1)) :  
        if (s1[i] == '0' and s2[i] == '1') : 
            c0 += 1;    
        elif (s1[i] == '1' and s2[i] == '0') : 
            c1 += 1;  
    result = c0 // 2 + c1 // 2;  
    if (c0 % 2 == 0 and c1 % 2 == 0) : 
        return result;  
    elif ((c0 + c1) % 2 == 0) : 
        return result + 2;  
    else : 
        return -1;