#include <iostream>
#include <vector>
#include <unordered_map>
#include <climits>
using namespace std;

const int MAXN = 100005;
int dp[(int)1e4+5][26];
int n, m;
char S[MAXN], T[MAXN];

unordered_map<char, vector<int>> positions;

int main() {
    cin >> n >> m;
    cin >> S + 1;
    cin >> T + 1;

   
    for (int i = 1; i <= n; ++i) {
        positions[S[i]].push_back(i);
    }

 
    for (int i = 0; i < m; ++i) {
        dp[i+1][T[i+1] - 'a'] = INT_MAX;
    }


    for (int i = 1; i <= m; ++i) {
        if (positions.find(T[i]) == positions.end()) {
            cout << -1 << endl;
            return 0;
        }
        for (int j = 0; j < 26; ++j) {
            dp[i][j] = INT_MAX;
        }
        for (int j = 0; j < positions[T[i]].size(); ++j) {
            int pos = positions[T[i]][j];
            for (int k = 0; k < 26; ++k) {
                if (i > 1) {
                    dp[i][k] = min(dp[i][k], dp[i-1][k] + 1 + abs(pos - positions[T[i-1]][0]));
                }
                dp[i][T[i] - 'a'] = min(dp[i][T[i] - 'a'], dp[i-1][j] + 1);
            }
        }
    }

 
    int minTime = INT_MAX;
    for (int i = 0; i < 26; ++i) {
        minTime = min(minTime, dp[m][i]);
    }

    cout << (minTime == INT_MAX ? -1 : minTime) << endl;
    return 0;
}

In file included from /usr/include/c++/4.8/unordered_map:35:0,
                 from answer.code:3:
/usr/include/c++/4.8/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
 #error This file requires compiler and library support for the \
  ^
answer.code:12:1: error: 'unordered_map' does not name a type
 unordered_ma...