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

char*mmap();
#define rd(v) int v=0;{int _c;while(_c=*rp++-48,_c>=0)v=v*10+_c;}

#define WTHI(v) {long _z=v,_n=0,_d=0;while(++_n,_d=_d<<8|0x30|_z%10,_z/=10);*(long*)wp=_d;wp+=_n;}
#define WTLO(v) {long _z=v,_n=8,_d=0;while(_d=_d<<8|0x30|_z%10,_z/=10,--_n);*(long*)wp=_d;wp+=8;}
#define wt(v) if(v>=100000000){WTHI(v/100000000);WTLO(v);}else{WTHI(v);}

#define min(a,b) (a<=b?a:b)

main(){
	long a,b;
	char*rp=mmap(0l,1l<<28,1,2,0,0ll);
	while(*rp++>=48);
	{
		rd(c);
		rd(d);
		a=c;
		b=a+c;
	}
	while(*rp){
		rd(c);
		rd(d);
		a=min(a+d,b)+c;
		b=min(a,b+d)+c;
	}
	char wbuf[32],*wp=wbuf;
	wt(b);
	write(1,wbuf,wp-wbuf);
	_exit(0);
}