#include <stdio.h>

int main()
{
        int c,p = -1;
        int co=0;
        
        while(1)
        {
            scanf("%d",&c);
            if(c == -1)
            break;
            
            if(c!=p)
            {
                c++;
                p=c;
            }
                
        }
        printf("%d",c);
}