#include<stdio.h>
FILE *in=fopen("joc8.in","r");
FILE *out=fopen("joc8.out","w");
int x,y,v[10000],n,ok,i;
int main()
{
fscanf(in,"%d",&x);fscanf(in,"%d",&y);
while(!feof(in)) fscanf(in,"%d",&v[++n]);
if(v[n]==0) fprintf(out,"0");
else
{
ok=1;
for(i=1;i<=n&&x<=y&&ok==1;i++)
	{
	if(v[i]==1){ok=0;fprintf(out,"%d",(x+y)/2);}
	if(v[i]==0&&i+1<=n)
		{
		i++;
		if(v[i]==0)	x=(x+y)/2+1;
		if(v[i]==1)	y=(x+y)/2-1;
		}
	}
}
return 0;
}