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



long rpn_eval(const char *expr, long vars[26], int *error) {
    // TODO: tokenise expr, run a stack machine over the tokens, and either
    //       return the single remaining value (with *error = 0) or set
    //       *error = 1 on any problem.
    (void)expr; (void)vars;
    *error = 1;
    return 0;
}


int main(void) {
    long vars[26] = {0};
    char line[512];
    while (fgets(line, sizeof(line), stdin) != NULL) {
        size_t len = strlen(line);
        while (len > 0 && (line[len-1] == '\n' || line[len-1] == '\r')) line[--len] = '\0';
        if (len == 0) continue;
        int assign_var = -1;
        char *expr = line;
        if (line[0] >= 'a' && line[0] <= 'z' && line[1] == ' ' && line[2] == '=' && line[3] == ' ') {
            assign_var = line[0] - 'a';
            expr = line + 4;
        }
        int err = 0;
        long result = rpn_eval(expr, vars, &err);
        if (err) {
            printf("error\n");
        } else if (assign_var >= 0) {
            vars[assign_var] = result;
            printf("%c = %ld\n", 'a' + assign_var, result);
        } else {
            printf("%ld\n", result);
        }
    }
    return 0;
}