#include <stdio.h>
#define N 10

int main(void){
    int n1 = 0, n2;
    
    while(1){
        scanf("%d ", &n2);
        if(n2-n1 != 1) break;
        n1 = n2;
    }
    printf("%d\n", n1+1);
    
    return 0;
}