// yukicoder 860 買い物
// 2019.9.22 bal4u

#include <stdio.h>

typedef long long ll;

int getchar_unlocked(void);
#define gc() getchar_unlocked()

int in() {   // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

inline static ll MIN(ll a, ll b) { return a <= b? a: b; }

int main()
{
	int N, C, D;
	ll s, t;

	N = in(); C = in(), D = in();
	t = C, s = t << 1;
	while (--N) {
		C = in(), D = in();
		t = MIN(t+D, s) + C;
		s = MIN(s+D, t) + C;
	}
	printf("%lld\n", s);
	return 0;
}