/*#include<stdio.h>
int main()
{
int i,j,k,n,m;
scanf("%d %d",&n, &m);
for(i=n; i<=m; i++)
{
for(j=1; j<=9; j++)
{
printf("%d*%d=%d\n",i,j,i*j);
}
}
}
*/
/*
int main()
{
int i,j,k,n;
scanf("%d",&k);
for(i=0; i<k; i++)
{
for(j=0; j<=i; j++)
{
printf("*");
}
printf("\n");
}
for(i=j; i>1; i--)
{
for(j=i; j>1; j--)
{
printf("*");
}
printf("\n");
}
return 0;
}
*/
/*#include<stdio.h>
int main()
{
int i,j,k,n;
scanf("%d",&n);
for(i=1; i<=n/2+1; i++)
{
for(j=n/2+1; j>i; j--)
{
printf(" ");
}
for(j=0; j<i*2-1; j++)
{
printf("*");
}
printf("\n");
}
}
*/
/*
#include <stdio.h>
int main()
{
int i,j,k,n;
scanf("%d %d",&n ,&k);
for( i=0; i<n; i++)
{
for( j=0; j<n; j++)
{
if( i==0 || j==0 || j==n-1 || i==n-1||(i+j+1)%k==0)
{
printf("*");
}
else
{
printf(" ");
}
}
printf("\n");
}
return 0;
}
*/
//(0,0) (0,1) (0,2) (0,3) (0,4) (0,5) (0,6) (0,7) (0,8) (0,9)
//(1,0) (1,1) (1,2) (1,3) (1,4) (1,5) (1,6) (1,7) (1,8) (1,9)
//(2,0) (2,1) (2,2) (2,3) (2,4) (2,5) (2,6) (2,7) (2,8) (2,9)
//(3,0) (3,1) (3,2) (3,3) (3,4) (3,5) (3,6) (3,7) (3,8) (3,9)
//(4,0) (4,1) (4,2) (4,3) (4,4) (4,5) (4,6) (4,7) (4,8) (4,9)
//(5,0) (5,1) (5,2) (5,3) (5,4) (5,5) (5,6) (5,7) (5,8) (5,9)
//(6,0) (6,1) (6,2) (6,3) (6,4) (6,5) (6,6) (6,7) (6,8) (6,9)
//(7,0) (7,1) (7,2) (7,3) (7,4) (7,5) (7,6) (7,7) (7,8) (7,9)
//(8,0) (8,1) (8,2) (8,3) (8,4) (8,5) (8,6) (8,7) (8,8) (8,9)
//(9,0) (9,1) (9,2) (9,3) (9,4) (9,5) (9,6) (9,7) (9,8) (9,9)
/*
int main() {
int a[100] = {0};
int i, n;
scanf("%d", &n);
for(i=0; i<n; i++) {
scanf("%d", &a[i]);
}
for(i=0; i<n; i++) {
printf("%d ", a[i]);
}
}
*/
/*
int main()
{
int a[1000];
int n,i;
scanf("%d",&n);
for(i=0; i<n; i++)
{
scanf("%d", &a[i]);
}
for(i=n-1; i>=0; i--)
{
printf("%d ",a[i]);
}
}
*/
/*
int main()
{
int a[100];
int n,i;
scanf("%d",&n);
for(i=0; i<n; i++)
{
scanf("%d",&a[i]);
}
for(i=0; i<n; i++)
{
printf("%d\n",a[i]);
}
for(i=0; i<n; i++)
{
printf("%d\n",a[i]);
}
}
*/
/*
int main()
{
int a[1000]={0};
int n,i,k;
scanf("%d",&n);
for(i=0; i<n; i++)
{
scanf("%d",&a[i]);
}
for(i=0; i<n; i++)
{
for(k=i;k<n+i;k++)
{
printf("%d ",a[k%n]);
}
printf("\n");
}
}
*/
/*
int main()
{
int a[10] = {0};
int n,i,k;
for(i=0;i<10;i++)
{
scanf("%d",&a[i]);
}
scanf("%d",&k);
printf("%d",a[k-1]);
}
*/
int main()
{
int i,j,k,n,s=0;
scanf("%d",&n);
for(k=1; k<=n; k++)
{
s+=k;
}
for(i=1;i<=n-1;i++)
{
scanf("%d",&j);
s-=j;
}
printf("%d",s);
}