#include <stdio.h>

int queue[100];
int f = 0;
int r = 0;

void enque(int x){
    queue[r++] = x;
}

int deque(){
    return queue[f++];
}

int empty(){
    return r == f;
}

int size(){
    return r - f;
}

int main() {
    enque(0);
    enque(3);
    
    enque(1);
    enque(4);
    
    enque(2);
    enque(2);

    int endtime = 0;
    int totalwait = 0;

    while (!empty()) {
        int start = deque();
        int work = deque(); 
        
        if (endtime < start) {
            endtime = start;
        }
        totalwait += endtime - start;
        endtime += work;
    }

    printf("%d", totalwait);
}