#include <cstdio>
const int MAXN = 1001;
int g[MAXN][MAXN], h[MAXN][MAXN], f[MAXN][MAXN];
int n, m, s, a[MAXN], b[MAXN];
inline int max(int x, int y) {
    return x>y ? x : y;
}
int main() {
    freopen("crossa.in","r",stdin);
    freopen("crossa.out","w",stdout);
    scanf("%d %d", &n, &m);
    for(int i=1; i<=n; i++)
        scanf("%d", a+i);
    for(int i=1; i<=m; i++)
        scanf("%d", b+i);
    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++) {
            g[i][j] = (j>1 && a[i] == b[j-1]) ? j-1 : g[i][j-1];
            h[i][j] = (i>1 && a[i-1] == b[j]) ? i-1 : h[i-1][j];
        }
    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++) {
            s = max(f[i-1][j], f[i][j-1]);
            if(g[i][j] > 0 && h[i][j] > 0 && a[i] != b[j])
                s = max(s, f[h[i][j]-1][g[i][j]-1] + 2);
            f[i][j] = s;
        }
    printf("%d\n", f[n][m]);
    return 0;
}