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

int main(int argc, char** argv){
  if(argc < 2){
    printf("Usage:\n\t%s \"S\"\n\t\tWhere S is a string in reverse polish notation.\n",argv[0]);
    return EXIT_SUCCESS;
  }

  double stack[512];
  double read;
  int size = 0;
  char* str = argv[1];
  char* rtn = NULL;
  stack[0] = 0;
  while(str != NULL && str[0] != '\0'){
    switch (str[0]) {
      case '0':
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
        read = strtod(str,&rtn);
        if(rtn != str){
          str = rtn;
          stack[size] = read;
          size++;
        }else{
          fprintf(stderr,"Error at position %ld\nUnable to read a number\n", str-argv[1]);
          return EXIT_FAILURE;
        }
        break;
      case '-': 
        if(str[1] != '\0' && str[1] >= '0' && str[1] <= '9'){
          read = strtod(str,&rtn);
          if(rtn != str){
            str = rtn;
            stack[size] = read;
            size++;
          }else{
            fprintf(stderr,"Error at position %ld\nUnable to read a number\n", str-argv[1]);
            return EXIT_FAILURE;
          }
        }else{
          if(size<2){
            fprintf(stderr,"Error at position %ld\nNot enough operands for substraction\n", str-argv[1]);
            return EXIT_FAILURE;
          }else{
            stack[size-2] = stack[size-2] - stack[size-1];
            size--;
            str++;
          }
        }
        break;
      case '*':
        if(size<2){
          fprintf(stderr,"Error at position %ld\nNot enough operands for multiplication (%d)\n", str-argv[1],size);
          return EXIT_FAILURE;
        }else{
          stack[size-2] = stack[size-2] * stack[size-1];
          size--;
          str++;
        }
        break;
      case '+':
        if(size<2){
          fprintf(stderr,"Error at position %ld\nNot enough operands for addition\n", str-argv[1]);
          return EXIT_FAILURE;
        }else{
          stack[size-2] = stack[size-2] + stack[size-1];
          size--;
          str++;
        }
        break;
      case '/':
        if(size<2){
          fprintf(stderr,"Error at position %ld\nNot enough operands for division\n", str-argv[1]);
          return EXIT_FAILURE;
        }else{
          stack[size-2] = stack[size-2] / stack[size-1];
          size--;
          str++;
        }
        break;
      default: str++; break;
    }
  }
  if(size > 1){
    fprintf(stderr,"Error: %d values left on the stack\n",size);
    return EXIT_FAILURE;
  }
  printf("%f\n",stack[0]);
  return EXIT_SUCCESS;
}