#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

#define rd_init() char*rp=({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd_skip() while(*rp++>=48)
#define wt(v) ({unsigned _z=v;do*--wp=_z%10+48;while(_z/=10);})
#define wt1(v) ({char wbuf[64],*wp=wbuf+sizeof wbuf;wt(v);write(1,wp,wbuf+sizeof wbuf-wp);})

int main(){
	rd_init();
	rd_skip();
	int a=1,b=1,x,z=0;
	while(x=*rp++,x!='\n'){
		x&=1;
		if(!a|!b){
			z+=!x;
			x=1;
		}
		a=b;
		b=x;
	}
	wt1(z);
	_exit(0);
}