calc e

#include <stdio.h>
#include <string.h>
#define MAX 1000
static void print(char *v1, char *v2, size_t size) {
  for (size_t i = 0; i < size; ++i) {
    printf("%d", v1[i]);
  }
  puts("");
  for (size_t i = 0; i < size; ++i) {
    printf("%d", v2[i]);
  }
  puts("");
}
int main(void) {
  char a[MAX] = {1, 0}, b[MAX] = {0}, c[MAX] = {0};
  c[0] = -1; // dummy
  for (int m = 1; memcmp(b, c, sizeof b); ++m) {
    // print(a, b, MAX);
    memcpy(c, b, sizeof c);
    for (size_t i = 0; i < MAX; ++i) {
      b[i] += a[i];
      for (size_t j = i; 1 <= j && 9 < b[j]; --j) {
        b[j] -= 10;
        ++b[j - 1];
      }
    }
    for (int i = 0, p = 0; i < MAX;
         p *= 10, p += a[i], a[i] = p / m, p %= m, ++i) {
      ;
    }
  }
  printf("%d.", b[0]);
  for (size_t i = 1; i < MAX; ++i) {
    printf("%d", b[i]);
  }
  puts("");
}