P1449 Postfix Expression

A postfix expression is an expression in which parentheses are not used, operators are placed after their two operands, and all computations are performed strictly from left to right in the order in which the operators appear (operator precedence does not need to be considered). In this problem, the operators include only $\texttt{+-*/}$. It is guaranteed that for the $\texttt{/}$ operation the divisor is not 0. In particular, the result of the $\texttt{/}$ operation should be truncated toward 0 (i.e., the same rule as C++ `/`). For example: $\texttt{3*(5-2)+7}$ corresponds to the postfix expression $\texttt{3.5.2.-*7.+@}$. In this expression, `@` is the end marker for the expression. `.` is the end marker for an operand.

Input a single line containing a string $s$, denoting the postfix expression.

Output a single integer, the value of the expression.

It is guaranteed that $1 \leq |s| \leq 50$, and the absolute value of the answer and of every intermediate value during computation does not exceed $10^9$. Translated by ChatGPT 5