bovites

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *insert( char *p, char *z, int x)

{
    char *kesz;
    int h1 = strlen(p),
        h2 = strlen(z);

    kesz = (char *) malloc ( (h1 + h2 + 1) * sizeof(char));
    memset(kesz, '\0', h1 + h2 + 1);

    if (h1 <= x)
    {
        strcpy(kesz, p);
        strcat(kesz, z);
        return kesz;
    }

    strncpy(kesz, p, x);
    strcat(kesz, z);
    strcat(kesz, &p[x]);

    return kesz;
}

#include <stdio.h>
#include <stdlib.h>
int main()
{
  char s1[ 1000 ], s2[ 1000 ];
  int n;
  char *insert( char *, char *, int );
  while ( scanf( "%s%s%d", s1, s2, &n ) != EOF )
  {
    char *p = insert( s1, s2, n );
    puts( p );
    free( p );
  }
  return EXIT_SUCCESS;
}