#include <iostream>
#include <string>
#include <stdlib.h>
using namespace std;

int main() {
    int pila[100];
    int tope = 0;
    
    string instr;
    
    while (cin >> instr) {
        if (instr == "PUSH") {
            int val;
            cin >> val;
            
            pila[tope] = val;
            tope += 1;
        } else if (instr == "ADD") {
            if (tope < 2) {
                abort();
            }
            
            int a = pila[tope - 1];
            int b = pila[tope - 2];
            
            tope -= 2;
            
            pila[tope] = a + b;
            tope += 1;
        } else if (instr == "PRINT") {
            if (tope < 1) {
                abort();
            }
            
            int val = pila[tope - 1];
            tope -= 1;
            
            cout << val << endl;
        } else if (instr == "DUP") {
            if (tope < 1) {
                abort();
            }
            
            int val = pila[tope - 1];
            pila[tope] = val;
            tope += 1;
        } else {
            cerr << "mala instruccion" << endl;
            abort();
        }
    }
}