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

char stack[100][100];
int top = -1;

void push(char *s) {
    strcpy(stack[++top], s);
}
char* pop() {
    return stack[top--];
}
int isOperator(char c) {
    return (c=='+' || c=='-' || c=='*' || c=='/' || c=='^');
}
int main() {
    char pre[100], op1[100], op2[100], temp[100];
    scanf("%s", pre);
    for (int i = strlen(pre) - 1; i >= 0; i--) {
        if (isalnum(pre[i])) {
            temp[0] = pre[i];
            temp[1] = '\0';
            push(temp);
        }
        else if (isOperator(pre[i])) {
            strcpy(op1, pop());
            strcpy(op2, pop());
            sprintf(temp, sizeof(temp), "%s%s%c", op1, op2, pre[i]);
            push(temp);
        }
            else {
                printf("Invalid input");
                return 0;
            }
        }
        printf("%s", pop());
        return 0;
    }