#include <ctype.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

typedef enum {S0, S1, S2, S3, S4, S5, S6, S7} State;

bool read_double(double* value) {
   int sign = 1;
   double factor = 1;
   long long unsigned int mantissa = 0;
   int exponent = 0;
   int expsign = 1;
   bool error = false;
   do {
      State state = S0;
      factor = 1; mantissa = 0; exponent = 0; sign = 1;
      int ch = EOF; error = false; bool finished = false;
      while (!finished && !error && (ch = getchar()) != EOF) {
	 switch (state) {
	    case S0:
	       if (ch == '+' || ch == '-') {
		  if (ch == '-') sign = -1;
		  state = S1;
	       } else if (isdigit(ch)) {
		  mantissa = ch - '0';
		  state = S2;
	       } else if (ch == '.') {
		  state = S3;
	       } else {
		  // stay at S0, skipping other text
	       }
	       break;
	    case S1:
	       if (isdigit(ch)) {
		  mantissa = ch - '0';
		  state = S2;
	       } else if (ch == '.') {
		  state = S3;
	       } else {
		  error = true;
	       }
	       break;
	    case S2:
	       if (isdigit(ch)) {
		  mantissa = mantissa * 10 + ch - '0';
	       } else if (ch == '.') {
		  state = S4;
	       } else if (ch == 'E' || ch == 'e') {
		  state = S5;
	       } else {
		  finished = true;
	       }
	       break;
	    case S3:
	       if (isdigit(ch)) {
		  mantissa = mantissa * 10 + ch - '0';
		  factor /= 10;
		  state = S4;
	       } else {
		  error = true;
	       }
	       break;
	    case S4:
	       if (isdigit(ch)) {
		  mantissa = mantissa * 10 + ch - '0';
		  factor /= 10;
	       } else if (ch == 'E' || ch == 'e') {
		  state = S5;
	       } else {
		  finished = true;
	       }
	       break;
	    case S5:
	       if (ch == '+' || ch == '-') {
		  if (ch == '-') {
		     expsign = -1;
		  }
		  state = S6;
	       } else if (isdigit(ch)) {
		  exponent = ch - '0';
		  state = S7;
	       } else {
		  error = true;
	       }
	       break;
	    case S6:
	       if (isdigit(ch)) {
		  exponent = ch - '0';
		  state = S7;
	       } else {
		  error = true;
	       }
	       break;
	    case S7:
	       if (isdigit(ch)) {
		  exponent = exponent * 10 + ch - '0';
	       } else {
		  finished = true;
	       }
	       break;
	 }
      }
      if (ch == EOF) {
	 if ((!error && state == S2) || state == S4 || state == S7) break;
	 return false;
      }
      if (!error) {
	 ungetc(ch, stdin);
      }
   } while (error);
   *value = (double) sign * mantissa * factor * pow(10, exponent * expsign);
   return true;
}

int main() {
   double x; /* input value, returned by read_double */
   double sum = 0; /* regular sum */
   double kahan_sum = 0; double c = 0; /* Kahan sum and compensation term */
   while (read_double(&x)) {
      /* regular sum */
      sum += x;
      /* Kahan sum */
      double y = x - c;
      double t = kahan_sum + y;
      c = (t - kahan_sum) - y;
      kahan_sum = t;
   }
   printf("Regular sum: %.17lg\n", sum);
   printf("Kahan sum:   %.17lg\n", kahan_sum);
   printf("Difference:  %lg\n", fabs(sum - kahan_sum));
}