import java.util.HashSet;

import java.util.Set;

public class FrogRiverOne {

public static void main(String[] args) {

int X = 3;

int[] A = {1, 3, 1, 3, 2, 1, 3};

Set positions = new HashSet();

for (int i = 1; i <= X; i++) {

positions.add(i);

}

Set currPositions = new HashSet();

for(int i = 0; i < A.length; i++) {

currPositions.add(A[i]);

if(positions.size() > currPositions.size()) continue;

if(currPositions.containsAll(positions)) {

System.out.println(i);

break;

}

}

System.out.println(-1);

}

}