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

#include <cstdio>

/* 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) {
    /* Open the input and output files. */
    FILE *input_file = fopen("tennisin.txt", "r");
    FILE *output_file = fopen("tennisout.txt", "w");

    /* Read the values of N, M, X, A, and B from input file. */
    fscanf(input_file, "%d%d", &N, &M);

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

    for (int i = 0; i < M; i++) {
        fscanf(input_file, "%d", &A[i]);
        fscanf(input_file, "%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 to the output file. */
    if (answer == -1) {
        fprintf(output_file, "FOREVER\n");
    } else {
        fprintf(output_file, "%lld\n", answer);
    }

    /* Finally, close the input/output files. */
    fclose(input_file);
    fclose(output_file);

    return 0;
}