rlm@0: 
rlm@0: #include <stdio.h>
rlm@0: #include <stdlib.h>
rlm@0: 
rlm@0: int main(int argc, char *argv[]){
rlm@0:   FILE *fp;
rlm@0:   int n;
rlm@0:   if((fp=fopen(argv[1] ,"r")) == NULL) {
rlm@0:     printf("Cannot open file.\n");
rlm@0:     exit(1);}
rlm@0:   fscanf(fp, "%d", &n); /* read from file */
rlm@0:   int answer = search_collatz(n);
rlm@0:   printf("%d\n", answer); }
rlm@0: 
rlm@0: long long collatz_next(long long n){
rlm@0:   if (!(n % 2)){
rlm@0:     return n/2;}
rlm@0:   else {
rlm@0:     return 1+(n*3);}}
rlm@0: 
rlm@0: int collatz_length(int n){
rlm@0:   long long t = n;
rlm@0:   int d = 1;
rlm@0:   while (t > 1){
rlm@0:     t = collatz_next(t);
rlm@0:     d++;}
rlm@0:   return d;}
rlm@0:   
rlm@0: int search_collatz(int n){
rlm@0:   int max = 0;
rlm@0:   int max_val = 0;
rlm@0:   int temp_val;
rlm@0:   int i;
rlm@0:   for (i = 1; i<n; i++){
rlm@0:     temp_val = collatz_length(i);
rlm@0:     if (temp_val > max_val){
rlm@0:       max = i;
rlm@0:       max_val = temp_val;}}
rlm@0:   return max;}
rlm@0: