#include <string.h>

/*
 * Concatenate s2 on the end of s1. s1 must be large enough.
 * Return s1.
 */

char *strcat(char *s1, const char *s2) {
    char *os1 = s1;
    while (*s1++) ;
    --s1;
    while (*s1++ = *s2++) ;
    return os1;
}
