hacker rank

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <stdbool.h>

struct stack_struct
{
    int elems[60000];
    int top;
};

void displayStack(struct stack_struct *st1);
bool isempty(struct stack_struct *st);
void push(struct stack_struct *st1, int elm);
int pop(struct stack_struct *st1);
void enqueue(struct stack_struct *st1, int elm);
void dequeue(struct stack_struct *st1, struct stack_struct *st2);
int top_elem(struct stack_struct *st1, struct stack_struct *st2);

int main() {

    int length = 0;
    scanf("%d",&length);
    
    struct stack_struct *s1 = (struct stack_struct *)malloc(sizeof(struct stack_struct));
    s1->top = 0;
    
    struct stack_struct *s2 = (struct stack_struct *)malloc(sizeof(struct stack_struct));
    s2->top = 0;
    
    for(int i = 0; i < length; i++){
        int query, ins_elm;
        scanf("%d",&query);
        
        if(query == 1){
            scanf("%d",&ins_elm);
            enqueue(s1, ins_elm);
        }
        else if(query == 2){
            dequeue(s1, s2);
        }
        else if(query == 3)
            printf("%d\n",top_elem(s1, s2));
    }
    
    return 0;
}

bool isempty(struct stack_struct *st)
{
    return st->top == 0 ? true : false;
}

void push(struct stack_struct *st1, int elm)
{
    st1->elems[st1->top++] = elm;
}

int pop(struct stack_struct *st1)
{
    if(isempty(st1))
        return -1;
    
    return st1->elems[--st1->top];
}

void enqueue(struct stack_struct *st1, int elm)
{
    push(st1, elm);
}

void dequeue(struct stack_struct *st1, struct stack_struct *st2)
{
    while(isempty(st1) == false){
        int push_elm = pop(st1);
        push(st2,push_elm);
    }
    
    int e = pop(st2);
    
    while(isempty(st2) == false){
        int push_elm = pop(st2);
        push(st1,push_elm);
    }
    
}

int top_elem(struct stack_struct *st1, struct stack_struct *st2)
{
    while(isempty(st1) == false){
        int push_elm = pop(st1);
        push(st2,push_elm);
    }
    
    int top_element = st2->elems[(st2->top) - 1];
    
    while(isempty(st2) == false){
        int push_elm = pop(st2);
        push(st1,push_elm);
    }
    
    return top_element;
}

void displayStack(struct stack_struct *st1)
{
    for(int i = 0; i < st1->top; i++){
        printf("%d\n",st1->elems[i]);
    }
}