#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() ({int _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define wt(v) ({ulong _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);})
#define repeat(e) for(typeof(e)_=e;_--;)
#define max(a,b) (a>=b?a:b)

typedef unsigned long ulong;

int main(){
	rd_init();
	int n=rd();
	long a0=0,a1=0;
	long b0=0,b1=0;
	repeat(n){
		long x=rd();
		long y=rd();
		long c=(x==a0?x:0)+b0;
		long d=(x==a1?x:0)+b1;
		long e=(y==a0?y:0)+b0;
		long f=(y==a1?y:0)+b1;
		a0=y;
		a1=x;
		b0=max(c,d)+(x==y?x:0);
		b1=max(e,f)+(x==y?x:0);
	}
	wt1(max(b0,b1));
	_exit(0);
}