#include <stdio.h>
#include <stdlib.h>

int n, ans;
int inSum, outSum;
int in[40], out[40];

int main(void) {
    scanf("%d", &n);

    for (int i = 1; i < n; ++i) {
        scanf("%d %d", &in[i], &out[i]);

        inSum += in[i];
        outSum += out[i];
    }

    for (in[0] = 0; in[0] <= outSum; ++in[0]) {
        // ∑a = ∑b
        out[0] = (inSum + in[0]) - (outSum);
        if (out[0] < 0) continue;

        // check ai <= ∑b - bi
        int ok = 1;
        int outSum2 = out[0] + outSum;

        for (int i = 0; i < n; ++i) {
            if (in[i] > outSum2 - out[i]) ok = 0;
        }

        if (ok) ++ans;
    }

    printf("%d\n", ans);
}