#include <stdio.h>
char str[600004];
char shi[300004];
int main(){
	long lN;
	long gt;
	int	num;
	int scc;
	scanf("%ld",&lN);
	for(long i=0L; i < lN; ++i){
		scanf("%d",&num);
		num += '0';
		str[ i + lN ] = str[ i ] = num;
	}
	scanf("%s",shi);
	for( gt=0;gt< lN; gt++ ) {
		scc = 1;
		for(long i=0L; i < lN-1; ++i){
			if( shi[i] == '>' ) {
				if( str[i+gt] < str[ i+gt+1 ] ) { scc=0; break; }
			} else {
				if( str[i+gt] > str[ i+gt+1 ] ) { scc=0; break; }
			}
		}
		if( scc ) break;
	}
	if( !scc ) gt = -1;
	printf("%ld\n", gt );
}