1423
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <math.h>
#include <limits.h>
 
using namespace std;
 
// Datatypes
typedef vector<int> vi; 
typedef vector<string> vs;
typedef vector<vi> vvi; 
typedef pair<int,int> ii; 
typedef long long ll;
typedef long double ld;
 
// Define
#define sz(a)             int((a).size()) 
#define pb                push_back 
#define all(c)            (c).begin(),(c).end() 
#define present(c,x)      ((c).find(x) != (c).end()) 
#define cpresent(c,x)     (find(all(c),x) != (c).end()) 
#define FOR(_i,_n)        for(int (_i) = 0; (_i) < (_n); (_i)++)
#define mp                make_pair
 
// Constants
const double eps = 1e-8; 
const double PI = 3.1415926535897932384626433832795;
 
#define INPUT_FILE "xo.in"
#define OUTPUT_FILE "xo.out"
 
#define N 2*250000
#define M 250000
 
char s[N+10];
char p[M+10];
int l[M+10];
int n;
int m;
 
int jump(int x, char c)
{
    while(1)
    {        
        if(p[x] == c) return (x+1);
        if(x == 0) return 0;
        x = l[x];
    }
}
 
void build()
{
    l[0] = l[1] = 0;
 
    for(int i = 2; i <= m; i++)
        l[i] = jump(l[i-1], p[i-1]);
}
 
int search()
{
    int q = 0;
 
    for(int i = 1; i < n; i++)
    {
        q = jump(q, s[i]);
 
        if(q == m)
        {
            /* found */
            return (i-m+1);
        }
    }
    return -1;
}
 
int main(void)
{
#ifdef ALEX
    freopen("input.in", "r", stdin);
    freopen("output.out", "w", stdout);
#else
    //freopen(INPUT_FILE, "r", stdin);
    //freopen(OUTPUT_FILE, "w", stdout);
#endif
 
    cin >> n;
    cin >> s;
    cin >> p;
 
    copy(s, s+n, s+n);
 
    m = n;
    n = 2*n;
 
    build();
 
    int offset;
 
    offset = search();
 
    if(offset == -1)
        cout << -1;
    else if(offset == 0)
        cout << 0;
    else
        cout << m-offset;
 
    return 0;
}
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