#include<stdio.h>
#include<string.h>
#include<ctype.h>
char stack[100][100];
int top=-1;
void push(char*str){
    strcpy(stack[++top],str);
}
char*pop(){
    return stack[top--];
}
int isOp(char c){
    return(c=='+'||c=='-'||c=='*'||c=='/'||c=='^');
}
int main(){
    char pre[100];
    scanf("%s",pre);
    int n=strlen(pre);
    for(int i=n-1;i>=0;i--){
        char c=pre[i],a[2]={c,'\0'},x[100],y[100],z[100];
        if(isalnum(c))push(a);
        else if(isOp(c)){
            if(top<1){
                printf("Invalid input");
                return 0;
            }
            strcpy(x,pop());
            strcpy(y,pop());
            printf(z,sizeof(z),"%c %s %s",c,x,y);
            push(z);
        }else{
            printf("Invalid input");
            return 0;
        }
    }
    if(top!=0)
    printf("%d",&top);
    else printf("%s",pop());
    return 0;
}