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#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <queue>
using namespace std;
#define MAXN 220
#define INF 0x3f3f3f3f
int n, m;
int dis[MAXN];
int vis[MAXN];
int mp[MAXN][MAXN];
int A, B;
void (int A)
{
memset(vis, 0, sizeof(vis));
memset(dis, INF, sizeof(dis));
dis[A] = 0;
for(int i = 1; i <= n; i++){
int MinNumber, Min = INF;
for(int j = 1; j <= n; j++) if(!vis[j] && dis[j] < Min){
Min = dis[j];
MinNumber = j;
}
vis[MinNumber] = 1;
for(int j = 1; j <= n; j++){
dis[j] = min(dis[j], dis[MinNumber] + mp[MinNumber][j]);
}
}
}
int main()
{
int k;
while(scanf("%d", &n) &&n){
scanf("%d %d", &A, &B);
memset(mp, INF, sizeof(mp));
for(int i = 1; i <= n; i++){
scanf("%d", &k);
if(i - k >= 1)
mp[i][i - k] = 1;
if(i + k <= n)
mp[i][i + k] = 1;
}
dijkstra(A);
if(dis[B] != INF)
printf("%dn", dis[B]);
else
printf("-1n");
}
return 0;
}
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