/*
#include <stdio.h>
int stack[100000]={};
int top=-1;
void push(int x)
{
top++;
stack[top]=x;
}
int pop()
{
if(top==-1)
return -1;
else
return stack[top--];
}
int main()
{
int n, h;
long long int sum=0;
scanf("%d", &n);
for(int i=0; i<n; i++)
{
scanf("%d", &h);
while(top!=-1&&h>=stack[top])
{
pop();
}
sum+=top+1;
push(h);
}
printf("%lld", sum);
return 0;
}
*/
#include <stdio.h>
int queue[1000]={};
int back=0, front=0;
void push(int a)
{
back++;
queue[back]=a;
}
int pop()
{
return queue[front++];
}
int main()
{
int k;
char n[201]={};
scanf("%d\n", &k);
for(int i=0; i<k; i++)
{
gets(n);
if(n[0]=='p'&&n[1] =='u'&&n[2]=='s'&&n[3]=='h')
{
int arr=0;
int x=strlen(n);
for(int j=6; j<x-2; j++)
{
arr*=10;
arr+=(n[j]-'0');
}
push(arr);
}
else if(n[0]=='f'&&n[1]=='r'&&n[2]=='o'&&n[3]=='n'&&n[4]=='t')
{
if(front==0)
{
printf("0\n");
}
else
{
printf("%d\n", queue[front]);
}
}
else if(n[0]=='b'&&n[1]=='a'&&n[2]=='c'&&n[3]=='k')
{
if(back==0)
{
printf("0\n");
}
else
{
printf("%d\n", queue[back]);
}
}
else if(n[0]=='p'&&n[1]=='o'&&n[2]=='p')
{
pop();
}
else if(n[0]=='s'&&n[1]=='i'&&n[2]=='z'&&n[3]=='e')
{
printf("%d\n", back-front);
}
else if(n[0]=='e'&&n[1]=='m'&&n[2]=='p'&&n[3]=='t'&&n[4]=='y')
{
if(back==front)
{
printf("true\n");
}
else
{
printf("false\n");
}
}
}
return 0;
}