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

void push(int x);
int pop(void);

int top, S[1000];
  
int main(){
  int a, b;
  char s[1000000];

  top = 0;
  
  while(scanf("%s", s) != EOF){
    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{
      push(atoi(s));
    }
  }
  
  printf("%d\n", pop());
  
  return 0;
}

void push(int x){
  if(top >= 999  ) printf("OverFllow\n");
  S[++top] = x;
}

int pop(){
  if(top == 0) printf("UnderFllow\n");
  top--;
  return S[top+1];
}