#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#define MAX 101
int stack[MAX],top=-1;
void push(int x){stack[++top]=x;}
int pop(){return stack[top--];}
int evaluate(char * seq){
    int n = strlen(seq)
    for(int i=n-1;i>=0;i--){
        char c = seq[i];
        if(isdigit(c))
        push(c -'0');
        else if(strchr("+-*/",c)){
            if(top<1)
            return -1;
            int a = pop().b = pop();
            inr r;
            if(c=='+')r=a+b;
            else if(c=='-')r=a-b;
            else if(c=='*')r=a*b;
            else if(c=='/'){if(b==0)return -1;r=a/b;}
            push(r);
        }else{
            return -1;
        }
    }
    return(top==0)?pop():-1;
    
}
int main(){
    
char seq[MAX];
fgets(seq,MAX,stdin);
seq[strcspn(seq,"\n")]=0;
int result=evaluate(seq);
if(result==-1)
printf("Invalid input\n");
else
printf("%d\n",result);
return 0;
}