There is one humidifier in the AtCoder company office. The current time is $0$, and the humidifier has no water inside.

You will add water to this humidifier $N$ times. The $i$-th addition of water ($1 \leq i \leq N$) takes place at time $T_i$, and you add $V_i$ liters of water. It is guaranteed that $T_i < T_{i+1}$ for all $1 \leq i \leq N-1$.

However, the humidifier has a leak, and as long as there is water inside, the amount of water decreases by $1$ liter per unit time.

Find the amount of water remaining in the humidifier immediately after you finish adding water at time $T_N$.

The input is given from Standard Input in the following format:

$N$

$T_1$ $V_1$

$T_2$ $V_2$

$\vdots$

$T_N$ $V_N$

Print the answer.

• $1 \leq N \leq 100$
• $1 \leq T_i \leq 100$ ($1 \leq i \leq N$)
• $1 \leq V_i \leq 100$ ($1 \leq i \leq N$)
• $T_i < T_{i+1}$ ($1 \leq i \leq N-1$)
• All input values are integers.

At each point in time, water is added as follows:

• Time $1$: Before adding, the humidifier has $0$ liters. After adding $3$ liters, it has $3$ liters.
• Time $3$: Before adding, it has $1$ liter. After adding $1$ liter, it has $2$ liters total.
• Time $4$: Before adding, it has $1$ liter. After adding $4$ liters, it has $5$ liters total.
• Time $7$: Before adding, it has $2$ liters. After adding $1$ liter, it has $3$ liters total.

After finishing the addition at time $7$, the humidifier contains $3$ liters. Thus, the answer is $3$.