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

#define MAX 1000
int top, S[MAX];

int isEmpty(){
  return top == 0;
}

int isFull(){
  return top >= MAX - 1;
}
  
void push(int x){
  if (isFull()) {
    printf("overflow\n");
    exit(1);
  }
  top++;
  S[top] = x;
}

int pop(){
  if(isEmpty()){
    printf("underflow");
    exit(1);
  }
  top--;
  return S[top+1];
}


int main(){
  int x,a,b;
  char s[100];
  top =0;
  
  while( scanf("%s", s) == 1 ){
    if ( s[0] == '+' ){
      a = pop();
      b = pop();
      push(a+b);
    } else if ( s[0] == '-' ){
      b = pop();
      a = pop();
      push(a-b);
    } else if ( s[0] == '*' ){
      a = pop();
      b = pop();
      push(a*b);
    } else {
      x = atoi(s);
      push(x);
    } 
  }
  printf("%d\n",pop());
  return 0;
}

