text: #include <stdio.h>
  #include <stdlib.h>
  
  typedef struct arr_string {
  	char** arr;
  	int size;
  } arr_string;
  
  char* summary(arr_string arr)
  {
    int i;
    int sum = 0;
    for (i=0; i<arr.size; ++i) {
      sum += strtol(*(arr.arr + i), NULL, 10);
    }
    char s[999999999];
    sprintf(s, "%ld", sum);
    return s;
  }
  
  int main(int argc, char **argv) {
    char s[] = "5091002802391387";
    printf("strtol(s) = %ld\n", strtol(s, NULL, 10));
    return 0;
  }
  