C++ :

#include<stdio.h>
int main()
{
    int n,a,b,c;
    while(scanf("%d",&n)!=EOF)
    {
        a=n/3600;
        b=n%3600/60;
        c=n%60;
        printf("%d:%d:%d\n",a,b,c);
    }
}

Pascal :

var a,b,c,d:integer;
begin
  readln(a);
  b:=a div 3600;
  c:=a mod 3600 div 60;
  d:=a mod 60;
  writeln(b,':',c,':',d);
end.