Toph - Arithmetic Sequence (Easy)

#include<stdio.h>
int main()
{
    int n;
    scanf("%d",&n);
    n=n*(n+1)/2;
    int q;
    scanf("%d",&q);
    while(q--)
    {
        int x;
        scanf("%d",&x);
        n-=x;
    }
    printf("%d\n",n);
    return 0;
}