#include <bits/stdc++.h>
int n;
bool a[100010];
char fd[1 << 23], *p(fd - 1);
inline int read() {
  while (*++p < 45)
    ;
  int x(*p & 15);
  while (*++p > 45) x = (x << 1) + (x << 3) + (*p & 15);
  return x;
}
signed main() {
  fread(fd, 1, 1 << 23, stdin), n = read();
  while (--n) a[read()] = 1;
  while (++n)
    if (!a[n]) return printf("%d\n", n), 0;
}
