/*
 * Solution Template for Tennis Robot II
 * 
 * Australian Informatics Olympiad 2024
 * 
 * This file is provided to assist with reading of input and writing of output
 * for the problem. You may modify this file however you wish, or
 * you may choose not to use this file at all.
 */

#include <stdio.h>

/* N is the number of bins. */
int N;

/* M is the number of instructions. */
int M;

/*
 * X contains the number of balls in each bin. Note that this array starts from
 * 1 (not 0), and so the values are X[1] to X[N].
 */
long long X[200005];

/*
 * A and B contain the instructions. Note that the arrays start from 0, and so
 * the instructions are (A[0], B[0]) to (A[M-1], B[M-1]).
 */
int A[200005];
int B[200005];

long long answer;
int main(void) {
    int i;

    /* Read the values of N, M, X, A, and B. */
    scanf("%d%d", &N, &M);

    /* Values in X are indexed from 1 to N (not 0 to N-1) */
    for (i = 1; i <= N; i++) {
        scanf("%lld", &X[i]);
    }

    for (i = 0; i < M; i++) {
        scanf("%d", &A[i]);
        scanf("%d", &B[i]);
    }

    /*
     * TODO: This is where you should compute your solution. Store the number
     * of instructions that the robot will successfully complete (or -1 if it
     * will run forever) into the variable answer.
     */

    /*
     * Please note that the answer may exceed the maximum value
     * that can be stored in an "int" integer type.
     * Because of this, you should use the "long long" integer type
     * instead of "int" when computing your solution.
     */

    /* Write the answer. */
    if (answer == -1) {
        printf("FOREVER\n");
    } else {
        printf("%lld\n", answer);
    }

    return 0;
}