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

#define rd_skip() while(*rp++>=48)
#define wt(v) {ulong _z=v;do*--wp=_z%10+48;while(_z/=10);}

typedef unsigned long ulong;

ulong f1(){
	char*mmap();
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd_skip();
	long d=1,y=1,b=0,a=*rp++;
	for(long c;c=*rp++,c>='A';){
		if(c!=a){
			if(d==1||c!=b){
				b=a;
				++d;
			}
			else{
				b^='R'^'G'^'B'^a;
				--d;
				++y;
			}
			a=c;
		}
	}
	return y+d*2/3;
}

void f2(ulong z){
	char wbuf[64],*wp=wbuf+sizeof wbuf;
	wt(z);
	write(1,wp,wbuf+sizeof wbuf-wp);
}

int main(){
	f2(f1());
	_exit(0);
}